| 1. |
- 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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| 2. |
- Carlstrom, C. F., et al.
(författare)
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Characterization of damage in InP dry etched using nitrogen containing chemistries
- 2001
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 19:5, s. 1905-1910
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Tidskriftsartikel (refereegranskat)abstract
- Etching of InP by different ion beam etching processes using chemistries containing nitrogen, such as nitrogen milling, N(CH3)(3) and Ar/N(CH3)(3) based reactive ion beam etching (RIBS), and N-2/CH4/H-2 based chemically assisted ion beam etching (CAIBE), is investigated. The residual surface damage is characterized using I-V characteristics of Au/InP metal-semiconductor (MS) contacts and photoluminescence (PL) yield measurements from near surface quantum wells and bulls InP. The contacts formed on as-etched surfaces, irrespective of the etch process, show ohmic behavior. On the other hand, although the PL yield is reduced for the different processes, the measured intensities show variations which are attributed to passivation of defects by hydrogen. Secondary ion mass spectroscopy (SIMS) was used to check (qualitatively) the presence of nitrogen in the etched and annealed InP samples. SIMS data show the presence of nitrogen in the near surface region of the etched samples, but nitrogen levels drop to background levels upon annealing at typical regrowth conditions (650 degreesC under phosphine flow). Interestingly, the annealing step results not only in a significant recovery of the PL yield, but also in a recovery of Schottky characteristics of the Au contacts formed on the annealed surfaces. These observations show that the etch-induced damage is significantly reduced by annealing and suggests recovery of the near-surface stoichiometry and possibly reduction of nitrogen-related defects.
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| 3. |
- Henschel, W, et al.
(författare)
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Fabrication of 12 nm electrically variable shallow junction metal-oxide-semiconductor field effect transistors on silicon on insulator substrates
- 2003
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 21:6, s. 2975-2979
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Tidskriftsartikel (refereegranskat)abstract
- Electrically variable shallow junction metal-oxide-semiconductor field effect transistors on silicon on insulator have been fabricated to evaluate the suitability of fabrication processes on a nanoscale. In addition, the limits of scalability have been explored reducing gate lengths down to 12 nm. Specific attention has been paid to the overlay accuracy as required for the fabrication of these double gate structures. The superior quality of hydrogen silsesquioxane (HSQ) as electron beam resist and as mask material is demonstrated. The transistor fabricated exhibits extremely low leakage currents and relatively high on currents. The 8 orders of magnitude difference between the on and off states demonstrates conclusively large potentials for metal-oxide-semiconductor structures with critical dimensions in the 10 nm regime. (C) 2003 American Vacuum Society.
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| 4. |
- Håkanson, Ulf, et al.
(författare)
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Electric field effects in single semiconductor quantum dots observed by scanning tunneling luminescence
- 2003
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 21:6, s. 2344-2347
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) and scanning tunneling luminescence were used to correlate the topography with the emission spectra from individual self-assembled, InP quantum dots (QDs). We have investigated in detail how the electric field induced by the STM tip affects the emission from the QDs. This was done when exciting a QD, by altering the bias for constant current, by altering the current for constant bias, or by changing the tip position. An increased bias (increased electric field) leads to Stark shift of the QD emission, whereas a larger tunneling current results in state filling of the emission. Furthermore, when exciting the QD, the position of the STM tip is shown to have large effects on the QD luminescence.
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| 5. |
- Håkanson, Ulf, et al.
(författare)
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Ultrahigh vacuum scanning probe investigations of metal induced void formation in SiO2/Si(111))
- 2002
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Ingår i: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 20:1, s. 226-229
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Konferensbidrag (refereegranskat)abstract
- Using scanning electron microscopy guidance, atomically resolved scanning tunneling microscopy investigations inside openings formed during the decomposition of a thick SiO2 film on a Si(111) surface have been performed. We report, for the first time, the presence of Ni atoms inside self-formed openings. The SiO2 decomposition as a function of annealing temperature and time was studied. By comparing self-formed and lithographically designed openings in the SiO2 layer we have shown that Ni contamination of the SiO2/Si(111) has a profound effect on the formation of self-induced lateral oxide openings. (C) 2002 American Vacuum Society.
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| 6. |
- Jacob, AP, et al.
(författare)
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Post-growth process relaxation properties of strained Cd0.92Zn0.08Te/Cd0.83Zn0.17Te quantum well heterostructures grown by molecular beam epitaxy
- 2004
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society; 1999. - 1071-1023 .- 1520-8567. ; 22:2, s. 565-569
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Tidskriftsartikel (refereegranskat)abstract
- The post-growth structural stability regarding relaxation and defect propagation in Cd0.83Zn0.17Te/Cd0.92Zn0.08Te/Cd0.83Zn0.17Te quantum well (QW) heterostructures grown on [001] oriented Cd0.88Zn0.12Te substrates at 300degreesC by molecular beam epitaxy is investigated. The investigated heterostructures were subjected to post-growth thermal treatment in an ambient atmosphere in a temperature range between 280 and 550degreesC for 3 It each. We have used high-resolution x-ray diffraction as the main characterization tool. High-resolution rocking curves as well as the powerful two-dimensional reciprocal space mapping were employed in both symmetrical as well as asymmetrical reflections. The results indicate that at a post-growth temperature cycle of 350degreesC for 3 h slight modification of the Cd0.83Zn0.17Te/Cd0.92Zn0.08Te barrier/QW heterointerface smoothness is affected. This indicates the onset of migration of Zn atoms at this post-growth temperature time cycle. At 450 degreesC, this effect is more pronounced and seen as the complete disappearance of thickness fringes. For higher post-growth thermal treatment at 550 degreesC for 3 h, a hi-fi relaxation level accompanied by Zn content reduction is observed. A reduction of the Zn content down to 0.11 fractional value in the thick Cd0.83Zn0.17Te barrier is attributed to Zn out diffusion and/or Zn precipitation. (C) 2004 American Vacuum Society.
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| 7. |
- Keil, M, et al.
(författare)
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Process development and characterization of antisticking layers on nickel-based stamps designed for nanoimprint lithography
- 2004
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 22:6, s. 3283-3287
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of different derivatives of fluorinated alkyl phosphoric acids have been deposited from aqueous solutions onto surfaces of oxidized polycrystalline nickel stamps. which are commonly used in several industrial applications of nanoimprint lithography (NIL). The films have been established in order to increase the antiadhesion tendencies at the stamp polymer interface. Thicknesses, chemical compositions, and purities of the films as well as binding mechanisms to the stamp surfaces have been determined by photoelectron spectroscopy (XPS). The results demonstrate the adsorption of highly pure films having thicknesses in the monomolecular region, whose chemical compositions are characterized by large ratios of fluorinated to nonfluorinated carbon species. The high ionic nature of Ni-oxide benefits strong ionic linkages between the phosphate groups of the fluorinated antisticking film and the stamp surface, allowing a large-scale production of imprints with patterned stamps having feature sizes down to 100 nm. (C) 2004 American Vacuum Society.
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| 8. |
- Maximov, Ivan, et al.
(författare)
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Investigation of polymethylmethacrylate resist residues using photoelectron microscopy
- 2002
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Ingår i: Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures. - : American Vacuum Society. - 1071-1023 .- 1520-8567 .- 0734-211X. ; 20:3, s. 1139-1142
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Konferensbidrag (refereegranskat)abstract
- Quantitative photoelectron spectromicroscopy has been used to study polymethylmethacrylate (PMMA) resist residues on SiO2 surfaces after electron beam exposure and resist development, It was found that correctly exposed and developed PMMA leaves residues with an average thickness of about 1 nm. Higher exposure doses result in the decrease in film thickness, but with residues of about 0.5 mn. The technique can be applied as a powerful tool for surface and interface quality control in technology of electronic devices.
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| 9. |
- Mulot, Mikael, et al.
(författare)
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Fabrication of two-dimensional InP-based photonic crystals by chlorine based chemically assisted ion beam etching
- 2004
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 22:2, s. 707-709
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional photonic crystals (PhCs) were etched into InP/(Ga,In)(As,P) planar waveguides using chlorine-based chemical assisted ion beam etching (CAIBE). The processed PhCs were optically characterized by measuring transmission through simple slabs and one-dimensional cavities. The optical performances inside the photonic band gap are much better compared to both previously reported CAIBE results and results obtained with other etching methods. In particular, we measured a record quality factor of 310 for one-dimensional cavities fabricated in this material system.
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| 10. |
- Mulot, M., et al.
(författare)
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Low-loss InP-based photonic-crystal waveguides etched with Ar/Cl-2 chemically assisted ion beam etching
- 2003
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 21:2, s. 900-903
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate low-loss photonic-crystal (PC) waveguides realized in InP by Ar/Cl-2 based chemically assisted ion,beam etching. The waveguides are obtained as line defects in a triangular lattice of holes etched through a three-layer InP/GaInAsP/InP heterostructure. By optimizing the etching parameters so that the physical and the chemical components are balanced we succeed in obtaining holes deeper than 2 mum even for a hole diameter as small as 220 nm. The quality of the PCs etched by two different process conditions is compared by using the shape and the position of one of the mode gaps as an assessment tool;The measured transmissions spectra indicate that the PC waveguides etched with an optimized process exhibit losses smaller than 1 dB/100 mum. This is to date the lowest loss value reported for PC waveguides in semiconductor heterostructures at optical communication wavelengths.
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