| 1. |
- Buyanova, Irina A., et al.
(författare)
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Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures
- 2007
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Ingår i: 2006 E-MRS Fall Meeting. - : Wiley. ; , s. 159-173
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Konferensbidrag (refereegranskat)abstract
- In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II-VIs (e.g. ZnMnSe/Zn(Cd)Se) and III-Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron-hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by efficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.
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| 2. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effects of hydrogen on the optical properties of ZnCdO/ZnO quantum wells grown by molecular beam epitaxy
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 261912-
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO/ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of 2H from a remote plasma causes a substantial improvement in radiative efficiency of the investigated structures. Based on transient PL measurements, the observed improvements are attributed to efficient passivation by hydrogen of competing nonradiative recombination centers via defects. This conclusion is confirmed from the ODMR studies.
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| 3. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
- 2005
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Konferensbidrag (refereegranskat)abstract
- Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaNxP1-x alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t2 component of the X3c (or L1c CBM or a level arising from a complex of N and H (in some form) are also discussed.
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| 4. |
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| 5. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Hydrogen passivation of nitrogen in GaNAs and GaNP alloys : How many H atoms are required for each N atom?
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:2, s. 021920-
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Tidskriftsartikel (refereegranskat)abstract
- Secondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the dominant mechanism for neutralization of N-induced modifications in the electronic structure of the materials. Though the exact number of H atoms involved in passivation may depend on the conditions of the H treatment and the host matrixes, it is generally found that more than three H atoms are required to bind to a N atom to achieve full passivation for both alloys. © 2007 American Institute of Physics.
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| 6. |
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| 7. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Mechanism for radiative recombination in ZnCdO alloys
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:26
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Tidskriftsartikel (refereegranskat)abstract
- Temperature dependent cw- and time-resolved photoluminescence combined with absorption measurements are employed to evaluate the origin of radiative recombination in ZnCdO alloys grown by molecular-beam epitaxy. The near-band-edge emission is attributed to recombination of excitons localized within band tail states likely caused by nonuniformity in Cd distribution. Energy transfer between the tail states is argued to occur via tunneling of localized excitons. The transfer is shown to be facilitated by increasing Cd content due to a reduction of the exciton binding energy and, therefore, an increase of the exciton Bohr radius in the alloys with a high Cd content. © 2007 American Institute of Physics.
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| 8. |
- Buyanova, Irina, 1960-, et al.
(författare)
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On spin injection in GaMnN/InGaN Light-Emitting Diodes
- 2004
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Ingår i: 3rd International Conference on Physics and Applications of Spin-Related Phenomena in Semiconductors PASPS III,2004.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Buyanova, Irina, 1960-, et al.
(författare)
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On the origin of spin loss in GaMnN/InGaN Light-Emitting Diodes
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84, s. 2599-
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Tidskriftsartikel (refereegranskat)abstract
- Spin polarization of GaMnN/InGaN light-emitting diodes grown by molecular beam epitaxy is analyzed. In spite of the ferromagnetic behavior of the GaMnN spin injector, the diodes are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN spin detector, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection.
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| 10. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical and electrical characterization of (Ga,Mn)N/InGaN multiquantum well light-emitting diodes
- 2004
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 33:5, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- (Ga,Mn)/N/InGaN multiquantum well (MQW) diodes were grown by molecular beam epitaxy (MBE). The current-voltage characteristics of the diodes show the presence of a parasitic junction between the (Ga,Mn)N and the n-GaN in the top contact layer due to the low conductivity of the former layer. Both the (Ga,Mn)N/InGaN diodes and control samples without Mn doping show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. The observed polarization is shown to correspond to the intrinsic optical polarization of the InGaN MQW, due to population distribution between spin sublevels at low temperature, as separately studied by resonant optical excitation with a photon energy lower than the bandgap of both the GaN and (Ga,Mn)N. This indicates efficient losses in the studied structures of any spin polarization generated by optical spin orientation or electrical spin injection. The observed vanishing spin injection efficiency of the spin light-emitting diode (LED) is tentatively attributed to spin losses during the energy relaxation process to the ground state of the excitons giving rise to the light emission.
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| 11. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical characterization of Zn(1-x)Cd(x)O alloys grown by molecular-beam epitaxy
- 2006
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Ingår i: 210th ECS Meeting Volume 3, Issue 5. - : The Electrochemical Society. ; , s. 391-398
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have carried out comprehensive optical studies to evaluate structural and bandgap properties of Zn1-xCdxO alloys with x{less than or equalto}0.17 grown by molecular beam epitaxy. High crystalline quality ofthe alloys was concluded from cathodoluminescence measurements. Based on absorptionand reflectance measurements, the compositional dependence of the bandgap energyof ZnCdO, estimated without taking into account excitonic effects, wasfound to follow the trend Eg(x)=3.28-2.23x+0.45x2. Degradation in the alloyquality due to possible phase separation was found to causedeviations from this trend, evident from a more rapid redshift of the absorption edge. Effects of Cd incorporation onthe variation of the bandgap energies with temperature are alsodiscussed.
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| 12. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical characterization of ZnMnO-based dilute magnetic semiconductor structures
- 2006
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 24:1, s. 259-262
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Tidskriftsartikel (refereegranskat)abstract
- n -type ZnMnO spin injection layers were grown by pulsed laser deposition on top of n-ZnMgOZnOp-AlGaNp-GaN hybrid spin light-emitting diode (LED) structures synthesized by molecular-beam epitaxy. Both the ZnMnOZnMgOZnOAlGaNGaN structures and control ZnMnO samples show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. This indicates difficulties in generating spin polarization by optical spin orientation or possible efficient spin losses. The results are similar to those found earlier for GaMnNInGaNAlGaN spin-LED structures and indicate that these wide-band-gap dilute magnetic semiconductors with weak spin-orbit interaction and hexagonal symmetry are not attractive for spin-LED applications. © 2006 American Vacuum Society.
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| 13. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical study of spin injection dynamics in InGaN/GaN quantum wells with GaMnN injection layers
- 2004
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 22:6, s. 2668-2672
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Tidskriftsartikel (refereegranskat)abstract
- The spin injection dynamics of GaMnN/InGaN multiquantum well (MQW) light emitting diodes (LEDs) grown by molecular beam epitaxy were examined using picosecond-transient and circularly polarized photoluminescence (PL) measurements. Even with the presence of a room temperature ferromagnetic GaMnN spin injector, the LEDs are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN MQW, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection. Typical photoluminescence decay times were 20-40 ns in both commercial GaN MQW LEDs with emission wavelengths between 420-470 nm and in the GaMnN/InGaN multi-quantum well MQW LEDs. In the wurtzite InGaN/GaN system, biaxial strain at the interfaces give rise to large piezoelectric fields directed along the growth axis. This built-in piezofield breaks the reflection symmetry of confining potential leading to the presence of a large Rashba term in the conduction band Hamiltonian which is responsible for the short spin relaxation times.
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| 14. |
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| 15. |
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| 16. |
- Buyanova, Irina, et al.
(författare)
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Spin dynamics in ZnO-based materials
- 2010
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Ingår i: Journal of Superconductivity and Novel Magnetism. - New York, USA : Springer-Verlag New York. - 1557-1939 .- 1557-1947. ; 23:1, s. 161-165
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we address the issue of spin relaxation and its relevance to spin detection in ZnO-based materials, by spin-polarized, time-resolved magneto-optical spectroscopy. We have found that spin relaxation is very fast, i.e. about 100 ps for donor bound excitons in wurtzite ZnO, despite of a weak spin–orbit interaction. We also reveal that alloying of ZnO with Cd enhances spin relaxation, prohibiting ZnCdO/ZnO structures for efficient optical spin detection. On the other hand, a variation in strain field induced by lattice mismatch with substrates does not seem to lead to a noticeable change in spin relaxation. The observed fast spin relaxation, together with the limitation imposed by the band structure, are thus identified as the two most important factors that limit the efficiency of optical spin detection in the studied ZnO-based materials.
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| 17. |
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| 18. |
- Chen, Weimin, 1959-, et al.
(författare)
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Dominant factors limiting efficiency of optical spin detection in ZnO-based materials
- 2008
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 092103-
-
Tidskriftsartikel (refereegranskat)abstract
- Two dominant factors limiting efficiency of optical spin detection in ZnO-based materials system are identified from time-resolved optical orientation and magneto-optical studies. The first is related to the fundamental band structure of the materials characterized by a weak spin-orbit interaction. It leads to cancellation of circular polarization from the optical transitions between the conduction band and the A and B valence band states, which would otherwise carry the desired information on spin polarization of carriers. The second limiting factor is shown to be efficient carrier/exciton spin relaxation, i.e., about 45-80 ps.
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| 19. |
- Chen, Weimin, 1959-, et al.
(författare)
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Efficient spin relaxation in InGaN/GaN and InGaN/GaMnN quantum wells : An obstacle to spin detection
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:19, s. 192107-
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Tidskriftsartikel (refereegranskat)abstract
- Transient magneto-optical spectroscopy of InGaNGaN and InGaNGaMnN quantum wells reveals a spin relaxation process with a characteristic time of 50 ps. We show that the observed spin relaxation is mediated by spin flips of individual carriers rather than by direct exciton spin flips, and is proposed to occur near the bottom of the exciton band (K=0). Nearly complete thermalization between spin sublevels of the excitons, observed immediately after the pulsed photoexcitation, is attributed to even faster spin relaxation of photogenerated hot carriers/excitons accompanying momentum and energy relaxation at high K vectors. © 2005 American Institute of Physics.
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| 20. |
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| 21. |
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| 22. |
- Chen, Weimin, 1959-, et al.
(författare)
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Prospects of potential semiconductor spin detectors
- 2007
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Ingår i: Advances in Nanomaterials and Processing, Pts 1 and 2. - : Trans Tech Publications Inc.. ; , s. 839-842
-
Konferensbidrag (refereegranskat)abstract
- We review our recent experimental findings by optical orientation spectroscopy that show efficient spin relaxation within semiconductor spin detectors to be an important factor limiting efficiency of spin injection in spin light-emitting structures based on ZnCdSe/ZnMnSe and InGaN/GaMnN. We provide evidence for the physical mechanism responsible for the observed efficient spin relaxation that accompanies momentum and energy relaxation of excitons/carriers. These findings call for increasing efforts in suppressing spin relaxation in spin detectors.
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| 23. |
- Chen, Weimin, 1959-, et al.
(författare)
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Spin depolarization in semiconductor spin detectors
- 2006
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Ingår i: Proc. of SPIE Vol. 6118. - : SPIE - International Society for Optical Engineering. ; , s. 611804-1-611804-12
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A brief review is given of our recent experimental results from in-depth investigations of spin depolarization and underlying physical mechanisms within semiconductor spin detectors based on II-VIs (e.g. Zn(Cd)Se quantum wells) and III-Vs (e.g. InGaN quantum wells), which are relevant to applications for spin-LEDs based on ZnMnSe/Zn(Cd)Se and GaMnN/InGaN structures. By employing cw and time-resolved magneto-optical and optical spin orientation spectroscopy in combination with tunable laser excitation, we show that spin depolarization within these spin detectors is very efficient and is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.
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| 24. |
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| 25. |
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| 26. |
- Chen, Weimin, 1959-, et al.
(författare)
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Spin relaxation in InGaN/Ga(Mn)N quantum wells
- 2005
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Ingår i: Bulletin of the American physical society. - 0003-0503. ; 50, s. 609-609
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Tidskriftsartikel (refereegranskat)abstract
- Proc. 2005 APS March Meeting, March 21-25, 2005; Los Angeles, CA, USA
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| 27. |
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| 28. |
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| 29. |
- Cho, H., et al.
(författare)
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High density plasma via hole etching in SiC
- 2001
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 19:4, s. 1878-1881
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Tidskriftsartikel (refereegranskat)abstract
- Throughwafer vias up to 100 mum deep were formed in 4H-SiC substrates by inductively coupled plasma etching with SF6/O-2 at a controlled rate of similar to0.6 mum min(-1) and use of Al masks. Selectivities of > 50 for SiC over Al were achieved. Electrical (capacitance-voltage: current-voltage) and chemical (Auger electron spectroscopy) analysis techniques showed that the etching produced only minor changes in reverse breakdown voltage, Schottky barrier height, and near surface stoichiometry of the SiC and had high selectivity over common frontside metallization. The SiC etch rate was a strong function of the incident ion energy during plasma exposure. This process is attractive for power SiC transistors intended for high current, high temperature applications and also for SiC micromachining.
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| 30. |
- Cho, H., et al.
(författare)
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Ultradeep, low-damage dry etching of SiC
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:6, s. 739-741
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (Phi(B)) and reverse breakdown voltage (V-B) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O-2 discharges on the near-surface electrical properties of SiC. For low ion energies (less than or equal to 60 eV) in the discharge, there is minimal change in Phi(B) and V-B, but both parameters degrade at higher energies. Highly anisotropic features typical of through-wafer via holes were formed in SiC using an Al mask.
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| 31. |
- Hong, J., et al.
(författare)
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Plasma chemistries for high density plasma etching of SiC
- 1999
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Ingår i: Journal of Electronic Materials. - Charlottesville, VA, USA. - 0361-5235 .- 1543-186X. ; 28:3, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- A variety of different plasma chemistries, including SF6, Cl2, ICI, and IBr, have been examined for dry etching of 6H-SiC in high ion density plasma tools (inductively coupled plasma and electron cyclotron resonance). Rates up to 4500 angstroms·min-1 were obtained for SF6 plasmas, while much lower rates (≀800 angstroms·min-1) were achieved with Cl2, ICI, and IBr. The F2-based chemistries have poor selectivity for SiC over photoresist masks (typically 0.4-0.5), but Ni masks are more robust, and allow etch depths ≥10 Όm in the SiC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000 angstroms·min-1) for SiC.
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| 32. |
- Kyrychenko, F.V., et al.
(författare)
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Investigation of a GaMnN/GaN/InGaN structure for spinLED
- 2005
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Ingår i: 27th Int. Conf. on the Physics of Semicond,2004. - : American Institute of Physics (AIP). - 0735402574 ; , s. 1319-1320
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Theoreticaland experimental studies of GaMnN/GaN/InGaN structure for a spin LEDdevice were performed. Strong electron spin relaxation was experimentally observedin a InGaN/GaN quantum well. It is shown that thestrong spin relaxation might result from the built-in piezoelectric fieldin strained wurzite heterostructures. A five level k · pmodel was used for microscopic calculations of the structure inversionasymmetry induced spin-orbit interaction. The magnitude of this interaction isshown to be comparable with that in InGaAs/GaAs quantum structures.©2005 American Institute of Physics
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| 33. |
- Lee, K. P., et al.
(författare)
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Comparison of F2 plasma chemistries for deep etching of SiC
- 2001
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Ingår i: Materials Research Society Symposium - Proceedings. - Boston, MA. ; , s. H7.7.1-H7.7.6
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Konferensbidrag (refereegranskat)abstract
- A number of F2-based plasma chemistries (NF3, SF6, PF5 and BF3) were investigated for high rate etching of SiC. The most advantageous of these is SF6, based on the high rate (0.6 Όm·min-) it achieves and its relatively low cost compared to NF3. The changes in electrical properties of the near-surface region are relatively minor when the incident ion energy is kept below approximately 75 eV. At a process pressure of 5 m Torr, the SiC etch rate falls-off by ∌15% in 30 Όm diameter via holes compared to larger diameter holes (> 60 Όm diameter) or open areas on the mask.
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| 34. |
- Leerungnawarat, P., et al.
(författare)
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Effect of UV light irradiation on SiC dry etch rates
- 2000
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 29:3, s. 342-346
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Tidskriftsartikel (refereegranskat)abstract
- Inductively Coupled Plasma etching of 4H-SiC under ultraviolet illumination was examined for SF6/Ar and Cl-2/Ar chemistries. Etch rate enhancements up to a factor of 8 were observed with UV light irradiation during Cl-2/Ar etching. The enhancement mechanism is related to photodesorption of SiClx and CClx species. Surface morphologies were unchanged as a result of the UV enhancement with Cl-2/Ar discharges. By contrast, there was no effect of UV irradiation on the SiC etch rates in SF6/Ar plasmas, but the surfaces were typically smoother than those obtained without the ultraviolet illumination. In the SF6/Ar chemistry the rate-limiting steps are either Si-C bond-breaking or supply of fluorine radicals to the surface, and not desorption of the SiFx and CFx etch products.
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| 35. |
- Leerungnawarat, P., et al.
(författare)
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Via-hole etching for SiC
- 1999
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 17, s. 2050-2054
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Tidskriftsartikel (refereegranskat)abstract
- Four different F2-based plasma chemistries for high-rate etching of SiC under inductively coupled plasma (ICP) conditions were examined. Much higher rates (up to 8000 #x2009; #xc5; #x2009;min-1) were achieved with NF3 and SF6 compared with BF3 and PF5, in good correlation with their bond energies and their dissociation efficiency in the ICP source. Three different materials (Al, Ni, and indium #x2013;tin oxide) were compared as possible masks during deep SiC etching for through-wafer via holes. Al appears to produce the best etch resistance, particularly when O2 is added to the plasma chemistry. With the correct choice of plasma chemistry and mask material, ICP etching appears to be capable of producing via holes in SiC substrates. #xa9; 1999 American Vacuum Society.
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| 36. |
- Lim, W., et al.
(författare)
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Migration and Luminescence Enhancement Effects of Deuterium in ZnO/ZnCdO Quantum Wells
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 032103-
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Tidskriftsartikel (refereegranskat)abstract
- ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ~0.8 µm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5 K and ~20 at 300 K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300 °C led to increased migration of 2H toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at >=400 °C as 2H was evolved from the sample (~90% loss by 500 °C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.
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| 37. |
- Norton, D.P., et al.
(författare)
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Ferromagnetism in ZnO Doped with Transition Metal Ions
- 2006. - 1
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Ingår i: ZnO Bulk, Thin Films and Nanostructures. - Oxford : Elsevier. - 9780080447223 - 0080447228 ; , s. 555-576
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- With an in-depth exploration of the following topics, this book covers the broad uses of zinc oxide within the fields of materials science and engineering: - Recent advances in bulk , thin film and nanowire growth of ZnO (including MBE, MOCVD and PLD), - The characterization of the resulting material (including the related ternary systems ZgMgO and ZnCdO), - Improvements in device processing modules (including ion implantation for doping and isolation ,Ohmic and Schottky contacts , wet and dry etching), - The role of impurities and defects on materials properties - Applications of ZnO in UV light emitters/detectors, gas, biological and chemical-sensing, transparent electronics, spintronics and thin film
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| 38. |
- Pearton, S. J., et al.
(författare)
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Ferromagnetism in transition-metal doped ZnO
- 2007
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 36:4, s. 462-471
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Forskningsöversikt (refereegranskat)abstract
- ZnO is an attractive candidate for spintronics studies because of its potential for exhibiting high Curie temperatures and the relative lack of ferromagnetic second phases in the material. In this paper, we review experimental results on transition-metal (TM) doping of ZnO and the current state of theories for ferromagnetism. It is important to re-examine some of the earlier concepts for spintronics devices, such as the spin field-effect transistor, to account for the presence of the strong magnetic field that has deleterious effects. In some of these cases, the spin device appears to have no advantage relative to the conventional charge-control electronic analog. We have been unable to detect optical spin polarization in ZnO.
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| 39. |
- Pearton, S.J., et al.
(författare)
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ZnO doped with transition metal ions
- 2007
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 54:5, s. 1040-1048
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Tidskriftsartikel (refereegranskat)abstract
- Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~ 15 at.%) and exhibits the anomalous Hall effect. ZnO is expected to be one of the most promising materials for room-temperature polarized light emission, but to date, we have been unable to detect the optical spin polarization in ZnO. The short spin relaxation time observed likely results from the Rashba effect. Possible solutions involve either cubic phase ZnO or the use of additional stressor layers to create a larger spin splitting in order to get a polarized light emission from these structures or to look at alternative semiconductors and fresh device approaches. © 2007 IEEE.
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| 40. |
- Polyakov, A. Y., et al.
(författare)
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Electrical and luminescent properties and the spectra of deep centers in GaMnN/InGaN light-emitting diodes
- 2004
-
Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 33:3, s. 241-247
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Tidskriftsartikel (refereegranskat)abstract
- Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external magnetic field (so-called -spin-LEDs-). The contact annealing temperature was kept to 750°C, which is the thermal stability limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and the n-GaN in the top contact layer.
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| 41. |
- Stehr, Jan Eric, et al.
(författare)
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Color center in ß-Ga2O3 emitting at the telecom range
- 2024
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 124:4
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal (TM) ions incorporated into a host from a wide bandgap semiconductor are recognized as a promising system for quantum technologies with enormous potential. In this work, we report on a TM color center in beta-Ga2O3 with physical properties attractive for quantum information applications. The center is found to emit at 1.316 mu m and exhibits weak coupling to phonons, with optically addressable higher-lying excited states, beneficial for single-photon emission within the telecom range (O-band). Using magneto-photoluminescence (PL) complemented by time-resolved PL measurements, we identify the monitored emission to be internal E-1 ->(3)A(2) spin-forbidden transitions of a 3d(8) TM ion with a spin-triplet ground state-a possible candidate for a spin qubit. We tentatively attribute this color center to a complex involving a sixfold coordinated Cu3+ ion.
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| 42. |
- Stehr, Jan Eric, et al.
(författare)
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Defects in N, O and N, Zn implanted ZnO bulk crystals
- 2013
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:10, s. 103509-
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Tidskriftsartikel (refereegranskat)abstract
- Comprehensive characterization of defects formed in bulk ZnO single crystals co-implanted with N and Zn as well as N and O atoms is performed by means of optically detected magnetic resonance (ODMR) complemented by Raman and photoluminescence (PL) spectroscopies. It is shown that in addition to intrinsic defects such as Zn vacancies and Zn interstitials, several N-related defects are formed in the implanted ZnO. The prevailed configuration of the defects is found to depend on the choices of the co-implants and also the chosen annealing ambient. Specifically, co-implantation with O leads to the formation of (i) defects responsible for local vibrational modes at 277, 511, and 581 cm−1; (ii) a N-related acceptor with the binding energy of 160 ± 40 meV that is involved in the donor-acceptor pair emission at 3.23 eV; and (iii) a deep donor and a deep NO acceptor revealed from ODMR. Activation of the latter defects is found to require post-implantation annealing in nitrogen ambient. None of these defects are detected when N is co-implanted with Zn. Under these conditions, the dominant N-induced defects include a deep center responsible for the 3.3128 eV PL line, as well as an acceptor center of unknown origin revealed by ODMR. Formation mechanisms of the studied defects and their role in carrier recombination are discussed.
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| 43. |
- Wang, J. J., et al.
(författare)
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High rate etching of SiC and SiCN in NF3 inductively coupled plasmas
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:5, s. 743-747
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Tidskriftsartikel (refereegranskat)abstract
- Etch rates of ∌3,500 Å/min for 6H-SiC and ∌7,500 Å/min for SiC0.5N0.5 were obtained in inductively coupled plasmas with NF3-based chemistries. Similar etch rate trends were achieved with both NF3/O2 and NF3/Ar mixtures. The rates were strong functions of plasma composition, ion energy and ion fluxes, and were independent of conductivity type for SiC. Surface root-mean-square (RMS) roughness were 1-2 nm for etched SiC over a wide range of conditions indicating equi-rate removal of the SiFx and CFx etch products, but SiCN surfaces became extremely rough (RMS roughness > 20 nm) for F2-rich plasma conditions. The etched surfaces of SiC were chemically clean and stoichiometric, with small (<0.2 at%) quantities of N2- or F2- containing residues detected. © 1998 Elsevier Science Ltd. All rights reserved.
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| 44. |
- Wang, J. J., et al.
(författare)
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ICP etching of SiC
- 1997
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Ingår i: Materials Research Society Symposium - Proceedings. - Boston, MA, USA. ; , s. 177-183
-
Konferensbidrag (refereegranskat)abstract
- A number of different plasma chemistries, including NF3/O2, SF6/O2, SF6/Ar, ICl, IBr, Cl2/Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 angstroms·cm-1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4) are volatile. Photoresist masks have poor selectivity over SiC in F2-based plasmas under normal conditions, and ITO or Ni are preferred.
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| 45. |
- Wang, J. J., et al.
(författare)
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ICP etching of SiC
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:12, s. 2283-2288
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Tidskriftsartikel (refereegranskat)abstract
- A number of different plasma chemistries, including NF3/O2, SF6/O2, SF6/Ar, ICl, IBr, Cl2/ Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in an inductively coupled plasma tool. Rates above 2000 Å cm-1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4) are volatile. Photoresist masks have poor selectivity over SiC in F2-based plasmas under normal conditions, and ITO or Ni is preferred. © 1998 Published by Elsevier Science Ltd. All rights reserved.
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| 46. |
- Wang, J. J., et al.
(författare)
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Inductively coupled plasma etching of bulk 6H-SiC and thin-film SiCN in NF3 chemistries
- 1998
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - 0734-2101 .- 1520-8559. ; 16:4, s. 2204-2209
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Tidskriftsartikel (refereegranskat)abstract
- A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin-film SiC0.5N0.5 in inductively coupled plasma (ICP) NF3/O2 and NF3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide masks display relatively good etch selectivity over SiC (maximum of ∌70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions. © 1998 American Vacuum Society.
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| 47. |
- Wang, J. J., et al.
(författare)
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Low damage, highly anisotropic dry etching of SiC
- 1998
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Ingår i: High Temperature Electronics Conference, 1998. HITEC. 1998 Fourth International. ; , s. 10-14
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Konferensbidrag (refereegranskat)abstract
- A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin film SiC0.5N0.5 in Inductively Coupled Plasma NF3/O2 and NF 3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide (ITO) masks display relatively good etch selectivity over SiC (maximum of 70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions
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| 48. |
- Wang, Xingjun, 1972-, et al.
(författare)
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Band gap properties of Zn1−xCdxO alloys grown by molecular-beam epitaxy
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 151909-
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Tidskriftsartikel (refereegranskat)abstract
- Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn1−xCdxO alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend Eg(x) = 3.37−2.82x+0.95x2. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications.
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| 49. |
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| 50. |
- Wang, Xingjun, et al.
(författare)
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Oxygen and zinc vacancies in as-grown ZnO single crystals
- 2009
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Ingår i: JOURNAL OF PHYSICS D-APPLIED PHYSICS. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 42:17, s. 175411-
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen and zinc vacancies are unambiguously shown to be formed in as-grown ZnO bulk crystals grown from melt without being subjected to irradiation, from electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) studies. Concentrations of the defects in their paramagnetic charge states V-O(+) and V-Zn(-) are estimated to be similar to 2 x 10(14) cm(-3) and similar to 10(15) cm(-3), respectively. The V-Zn(-) defect is concluded to act as a deep acceptor and to exhibit large Jahn-Teller distortion by 0.8 eV. The energy level of the defect corresponding to the (2-/-) transition is E-v + 1.0 eV. The isolated Zn vacancy is found to be an important recombination centre and is concluded to be responsible for the red luminescence centred at around 1.6 eV. On the other hand, the oxygen vacancy seems to be less important in carrier recombination as it could be detected only in EPR but not in ODMR measurements. Neither isolated V-Zn(-) nor V-O(+) centres participate in the so-called green emission. It is also shown that whereas the concentrations of both defects can be reduced by post-growth annealing, the Zn vacancy exhibits higher thermal stability. The important role of residual contaminants such as Li in the annealing process is underlined.
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