| 1. |
- Barrios, C. A., et al.
(författare)
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Epitaxially regrown GaAs/AlGaAs laser mesas with semi-insulating GaInP : Fe and GaAs : Fe
- 2001
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 30:8, s. 987-991
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Tidskriftsartikel (refereegranskat)abstract
- Selective regrowth of semi-insulating iron-doped Ga0.51In0.49P (SI-GaInP:Fe) and SI-GaAs:Fe around GaAs/AlGaAs mesas by hydride vapor phase epitaxy (HVPE) has been achieved. A HCl based in-situ cleaning procedure has been used to remove aluminum oxide from the etched walls of the mesas. Regrowth conducted without proper cleaning results in an irregular interface with voids. Regrowth morphology aspects are also presented. Our cleaning and regrowth methods have been used for fabricating GaAs/AlGaAs buried heterostructure in-plane lasers and vertical-cavity surface-emitting lasers.
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| 2. |
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| 3. |
- Broitman, E, et al.
(författare)
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Letter: Electrical properties of carbon nitride thin films : Role of morphology and hydrogen content
- 2002
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 31:9, s. 957-961
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The influence of hydrogen content and ambient humidity on the electrical properties of carbon nitride (CNX) films deposited by reactive magnetron sputtering from a graphite target in Ar discharges mixed with N-2 and H-2 at a substrate temperature of 350degreesC have been investigated. Carbon films deposited in pure Ar exhibit a dark resistivity at room temperature of similar to4 X 10(-2) Omegacm, while the resistivity is one order of magnitude lower for CN0.25 films deposited in pure N-2, due to their denser morphology. The increasing H-2 fraction in the discharge gas leads to an increased resistivity for all gas mixtures. This is most pronounced for the nitrogen-free films deposited in an Ar/H-2 mixture, where the resistivity increases by over four orders of magnitude. This can be related to a decreased electron mobility as H inhibits the formation of double bonds. After exposure to air, the resistivity increases with time through two different diffusion regimes. The measured electrical properties of the films are related to the apparent film microstructure, bonding nature, and ambient humidity.
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| 4. |
- 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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| 5. |
- Ciechonski, Rafal, et al.
(författare)
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Effect of boron on the resistivity of compensated 4H-SiC
- 2003
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Ingår i: Journal of electronic materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 32:5, s. 452-457
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Tidskriftsartikel (refereegranskat)abstract
- High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.
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| 6. |
- Danielsson, E., et al.
(författare)
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Inductively coupled plasma etch damage in 4H-SiC investigated by Schottky diode characterization
- 2001
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 30:3, s. 247-252
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Tidskriftsartikel (refereegranskat)abstract
- Ti Schottky diodes have been used to investigate the damage caused by inductively coupled plasma (ICP) etching of silicon carbide. The Schottky diodes were characterized using TV and CV measurements. An oxidation approach was tested in order to anneal the damage, and the diode characterization was used to determine the success of the annealing. The barrier height, leakage current, and ideality factor changed significantly on the sample exposed to the etch. When the etched samples were oxidized the electrical properties were recovered and were similar to the unetched reference sample (with oxidation temperatures ranging from 900 degreesC up to 1250 degreesC). Annealing in nitrogen at 1050 degreesC did not improve the electrical characteristics. A low energy etch showed little influence on the electrical characteristics, but since the etch rate was very low the etched depth may not be sufficient in order to reach a steady state condition for the surface damage.
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| 7. |
- Keiper, D., et al.
(författare)
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Growth of quaternary InP-based materials by LP-MOVPE using TBA and TBP in N-2 ambient
- 2000
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 29:12, s. 1398-1401
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the growth of quaternary In1-xGaxAsyP1-y/InP materials using TEA and TBP in a N-2 ambient. This process improves significantly the uniformity of In1-xGaxAs/InP QWs whereas it does not improve the quaternary Q(1.3)/InP uniformity compared to the conventional process utilizing AsH3 and PH3 in H-2. The effect on the x and y uniformity for different combinations of the group-V precursors TBA, TBP, PH3, and AsH3 with the carrier gases H-2 and N-2 is evaluated. Advantages with the TBA/TBP/N-2 process are discussed.
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| 8. |
- Lee, S. K., et al.
(författare)
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Ohmic contact formation on inductively coupled plasma etched 4H-silicon carbide
- 2002
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 31:5, s. 340-345
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Tidskriftsartikel (refereegranskat)abstract
- We report on the investigation of ohmic contact formation using sputtered titanium-tungsten contacts on an inductively coupled plasma (ICP) etch-damaged 4H-SiC surface. Transfer length method (TLM) measurements were performed to characterize how ICP-etch damage affects the performance of ohmic contacts to silicon carbide. In order to recover etch damage, high-temperature oxidation (1250degreesC for 1 h) was evaluated for one of the samples. Some of the etch damage was recovered, but it did not fully recover the etch damage for the sample etched with medium platen power (60 W). From our TLM measurements, the specific contact resistance (rho(C) of sputtered titanium tungsten on highly doped n(+)-type 4H-SiC epilayers with a doping of 1.1 X 10(19) cm(-3) for the unetched reference sample, 30-W etched, and 60-W etched with and without sacrificial oxidation was as low as 3.8 X 10(-5) Omegacm(2), 3.3 X 10(-5) Omega cm(2), 2.3 X 10(-4) Omegacm(2), and 1.3 X 10(-3) Omegacm(2), respectively. We found that the low-power (30 W) ICP-etching process did not affect the formation of ohmic contacts, and we did not observe any difference between the unetched and the 30-W etched sample from our TLM measurements, having the same value of the rho(C). However, medium-platen-power (60 W) ICP etching showed significant influence on the ohmic contact formation. We found that the specific contact resistance is highly related to the surface roughness and quality of the metals, and the lower, specific contact resistance is due to the smoother and denser ohmic contacts.
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| 9. |
- Lee, S. K., et al.
(författare)
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Schottky barrier height dependence on the metal work function for p-type 4H-silicon carbide
- 2001
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 30:3, s. 242-246
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Tidskriftsartikel (refereegranskat)abstract
- We investigated Schottky barrier diodes of several metals (Ti, Ni, and Au) having different metal work functions to p-type 4H-SiC (0001) using I-V and C-V characteristics. Contacts showed excellent Schottky behavior with stable ideality factors of 1.07, 1.23, and 1.06 for Ti, Ni, and Au, respectively, in the range of 24 degreesC to 300 degreesC. The measured Schottky barrier height (SBH) was 1.96, 1.41, and 1.42 eV for Ti, Ni, and Au, respectively, in the same temperature range from IV characteristics. Based on our measurements for p-type 4H-SiC, the SBH (phi (Bp)) and metal work functions (phi (m)) show a linear relationship of phi (Bp) = 4.58 - 0.61 phi (m) and phi (Bp) = 4.42 - 0.54(phim) for I-V and C-V characteristics at room temperature, respectively. We observed that the SBH strongly depends on the metal work function with a slope (S = phi (Bp)/phi (m)) of 0.58 even though the Fermi level is partially pinned. We found the sum of the SBH (phi (Bp) + phi (Bn) = E-g) at room temperature for nand p-type 4H-SiC to be 3.07 eV, 3.12 eV, and 3.21 eV for Ti, Ni, and Au, respectively, using I-V and C-V measurements, which are in reasonable accord with the Schottky-Mott limit.
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| 10. |
- 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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| 11. |
- Li, Z-F, et al.
(författare)
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Determination of carrier-transfer length from side-wall quantum well to quantum wire by micro-photoluminescence scanning
- 2003
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Ingår i: Journal of Electronic Materials. - : Springer Science Business Media. - 0361-5235 .- 1543-186X. ; 32:8, s. 913-916
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Tidskriftsartikel (refereegranskat)abstract
- Micro-photoluminescence (mu-PL) line scanning across a single V-groove, GaAs/AlGaAs quantum wire (QWR) has been performed at room temperature, revealing a clear spatial-dependence of the PL. After fitting each PL spectrum by multi-Gaussian line shapes, intensity profiles of each PL component from confined structures have been obtained as functions of the scanning position. The PL quenching of a side-wall quantum well (SQWL) has been recognized in a certain area in the vicinity of the QWR and is interpreted by carrier transfer into the QWR within effective transfer length. By simulating the carrier-transfer process from SQWL to QWR as a convolution of a step function for carrier distribution and a Gaussian function for exciting laser irradiance, the effective transfer length of about 1.8+/-0.3 mum has, therefore, been concluded.
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| 12. |
- Lundberg, N., et al.
(författare)
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CVD-based tungsten carbide Schottky contacts to 6H-SiC for very high-temperature operation
- 2000
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 29:3, s. 372-375
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Tidskriftsartikel (refereegranskat)abstract
- In this study, tungsten carbide, with its hardness, chemical inertness, thermal stability and low resistivity (25 mu Omega cm)(1) is shown as a reliable contact material to n- and p-type 6H-SiC for very high temperature applications. WC films with thicknesses of 100-150 nm were deposited by chemical vapor deposition (CVD) from a WF6/C3H8/H-2 mixture at 1173 K. A method to pattern CVD-tungsten carbide is suggested. TEM analysis of as deposited samples displayed a clear and unreacted interface. The electrical investigations of the p-type 6H-SiC Schottky contacts revealed a high rectification ratio and a low reverse current density (6.1 x 10(-5) A cm(-2), -10 V) up to 713 K. On n-type, a low barrier (Phi(Bn) = 0.79 eV) at room temperature was observed. The low Phi(Bn) value suggests WC to be promising as an ohmic contact material on highly doped n-type epi-layers. We will show a temperature dependence for the barrier height of tungsten carbide contacts that can be related to the simultaneous change in the energy bandgap, which should be considered when designing SiC devices intended for high temperature operation.
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| 13. |
- Paskova, Tanja, et al.
(författare)
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Hydride vapor-phase epitaxial GaN thick films for quasi-substrate applications : Strain distribution and wafer bending
- 2004
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 33:5, s. 389-394
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Tidskriftsartikel (refereegranskat)abstract
- The strain distribution in thick hydride vapor-phase epitaxial (HVPE)-GaN layers grown on metal-organic vapor-phase epitaxial GaN templates was studied by means of photoluminescence, x-ray mapping, and lattice parameter analysis. A variable temperature x-ray study of the film curvature was used for verification of the strain type. The relation between the strain inhomogeneity and the wafer bending in films residing on sapphire and freestanding on the thickness of the layer and the substrate is analyzed. Possibilities to improve the uniformity of the film characteristics and to reduce the bending of the HVPE-GaN films are discussed.
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| 14. |
- 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
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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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| 15. |
- Soderstrom, D., et al.
(författare)
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Dopant diffusion and current-voltage studies on epitaxial InP codoped with Ru and Fe
- 2001
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 30:8, s. 972-976
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Tidskriftsartikel (refereegranskat)abstract
- Semi-insulating Fe and Ru codoped InP epitaxial layers grown by low-pressure hydride vapor phase epitaxy have been investigated. InP:Ru and InP:Fe,Ru layers were grown on p-InP:Zn and n-InP:S substrates, in order to study dopant diffusion and electrical characteristics. Dopant diffusion profiles of Ru, Fe and Zn were measured by secondary ion mass spectroscopy. A small but noteworthy diffusion front is observed when InP:Ru is adjacent to InP:Zn, but not when adjacent to n-InP. For InP:Fe codoped with Ru a pronounced interdiffusion of Fe and Zn is observed for Ru concentrations less than 2 X 10(17) cm(-3), but, for a higher Ru concentration the interdiffusion is clearly suppressed. Moreover, when InP is codoped with Fe and Ru, the small diffusion tail of Ru in InP:Zn vanishes. Unlike InP:Fe, resistivities above 1 X 10(8) Ohm cm are measured for both electron and hole-current injection in InP:Fe,Ru.
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| 16. |
- Virojanadara, Chariya, et al.
(författare)
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Schottky barrier height studies of Au/4H-SiC(0001) using photoemission and synchrotron radiation
- 2002
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 31:12, s. 1353-1356
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (SBH) of Au on 4H-SiC(0001) has been studied using photoemission and synchrotron radiation. The Au was deposited in-situ on clean and well-ordered root3 X roots R30degrees reconstructed SiC surfaces prepared by in situ heating at similar to950degreesC. The SBH was determined from the shift observed in the Si 2p core level, in addition to the initial band bending determined for the clean surface. The results were compared with values obtained by electrical, capacitance-voltage (C-V), and current-voltage (I-V) characterization methods. A favorable comparison between the three independent, SBH determination methods was found.
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| 17. |
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| 18. |
- Lundberg, N, et al.
(författare)
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CVD-based tungsten carbide Schottky contacts to 6H-SiC for very high-temperature operation
- 2000
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Ingår i: JOURNAL OF ELECTRONIC MATERIALS. - 0361-5235. ; 29:3, s. 372-375
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Tidskriftsartikel (refereegranskat)abstract
- In this study, tungsten carbide, with its hardness, chemical inertness, thermal stability and low resistivity (25 mu Omega cm)(1) is shown as a reliable contact material to n- and p-type 6H-SiC for very high temperature applications. WC films with thickne
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