First principles study of hBN-AlN short-period superlattice heterostructures

We report a theoretical study of the structural, electronic and optical properties of hBN-AlN superlattice heterostructures (SL) using a first-principles approach based on standard and hybrid Density Functional Theory. We consider short-period ($L<10$ nm) SL and find that their properties depend strongly on the AlN layer thickness $L_{AlN}$. For $L_{AlN}\lesssim1$ nm, AlN stabilizes into the hexagonal phase and SL display insulating behavior with type II interface band alignment and optical gaps as small as $5.2$ eV. The wurtzite phase forms for thicker AlN layers. In these cases built-in electric fields lead to formation of polarization compensating charges as well as two-dimensional conductive behavior for electronic transport along interfaces. We also find defect-like states localized at interfaces which are optically active in the visible range.Comment: 5 pages, 5 figures + Suppl. Mat., to appear in Appl. Phys. Let

Interband Tunneling for Hole Injection in III-Nitride Ultra-violet Emitters

Ultra-violet emitters have several applications in the areas of sensing, water purification, and data storage. While the III-Nitride semiconductor system has the band gap region necessary for ultraviolet emission, achieving efficient ultraviolet solid state emitters remains a challenge due to the low p-type conductivity and high contact resistance in wide band gap AlGaN-based ultra-violet light emitters. In this work, we show that efficient interband tunneling can be used for non-equilibrium injection of holes into ultraviolet emitters. Polarization-engineered tunnel junctions were used to enhance tunneling probability by several orders of magnitude over a PN homojunction, leading to highly efficient tunnel injection of holes to ultraviolet light emitters. This demonstration of efficient interband tunneling introduces a new paradigm for design of ultra-violet light emitting diodes and diode lasers, and enables higher efficiency and lower cost ultra-violet emitters.Comment: 13 pages, 7 figures, Submitte

Enhancement of Rabi Splitting in a Microcavity with an Embedded Superlattice

We have observed a large coupling between the excitonic and photonic modes of an AlAs/AlGaAs microcavity filled with an 84-({\rm {\AA}})/20({\rm {\AA}}) GaAs/AlGaAs superlattice. Reflectivity measurements on the coupled cavity-superlattice system in the presence of a moderate electric field yielded a Rabi splitting of 9.5 meV at T = 238 K. This splitting is almost 50% larger than that found in comparable microcavities with quantum wells placed at the antinodes only. We explain the enhancement by the larger density of optical absorbers in the superlattice, combined with the quasi-two-dimensional binding energy of field-localized excitons.Comment: 5 pages, 4 figures, submitted to PR

High Pressure Flange Design

This research report summarizes high pressure flange design techniques and considerations utilized by Pratt & Whitney Aircraft, Florida Research & Development Center, during its development programs for high pressure liquid rocket engines. The report covers: 1) Aspects of cooling, heating, pressure, and external loading with design safety factors 2) Cantilever type flanges optimized for weight 3) Seals and fastener considerations for 6000 psi environment 4) An example high pressure, cryogenic cantilever flange desig

The Growth and Doping of Al(As)Sb by Metal-Organic Chemical Vapor Deposition

AbstractAlSb and AlAsxSb1−x epitaxial films grown by metal-organic chemical vapor deposition were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500°C and 76 torr using trimethylamine or ethyldimethylamine alane and triethylantimony. We examined the growth of AlAsSb using temperatures of 500 to 600 ° C, pressures of 65 to 630 torr, V/Ill ratios of 1–17, and growth rates of 0.3 to 2.7 μm/hour in a horizontal quartz reactor. SIMS showed C and 0 levels below 2 × 1018 cm−3 and 6×1018 cm−3 respectively for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn-doped AlAs0.16 Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between l×1017 cm−3 to 5×1018 cm−3 for Zn-doped material and electron concentrations in the low to mid 1018 cm−3 for Sndoped material. We have grown pseudomorphic InAs/InAsSb quantum well active regions on AlAsSb cladding layers. Photoluminescence of these layers has been observed up to 300 K.</jats:p

The Growth of InAsSb/InAsP Strained-Layer Superlattices for Use in Infrared Emitters

We describe the metal-organic chemical vapor deposition growth of InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. These SLSs were grown at 500{degrees}C, and 200 torr in a horizontal quartz reactor using TMIn, TESb, AsH{sub 3},and PH{sub 3}. By changing the layer thickness and composition we have prepared structures with low temperature ({le}20K) photoluminescence wavelengths ranging from 3.2 to 4.4 {mu}m. Excellent performance was observed for an SLS LED and both optically pumped and electrically injected SLS lasers. An optically pumped, double heterostructure laser emitted at 3.86 {mu}m with a maximum operating temperature of 240 K and a characteristic temperature of 33 K. We have also made electrically injected lasers and LEDs utilizing a GaAsSb/InAs semi-metal injection scheme. The semi-metal injected, broadband LED emitted at 4 {mu}m with 80 {mu}W of power at 300K and 200 mA average current. The InAsSb/InAsP SLS injection laser emitted at 3.6 gm at 120 K

Recent Advances in Mid-Infrared (3--6 Micron) Emitters

The authors describe the metal-organic chemical vapor deposition (MOCVD) of InAsSb/InAs multiple quantum well (MQW) and InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. They have made gain-guided, injection lasers using undoped, p-type AlAs{sub 0.16}Sb{sub 0.84} for optical confinement and both strained InAsSb/InAs MQW and InAsSb/InAsP SLS active regions. The lasers and LEDs utilize the semi-metal properties of a p-GaAsSb/n-InAs heterojunction as a source for electrons injected into active regions. A multiple-stage LED utilizing this semi-metal injection scheme is reported. Gain-guided, injected lasers with a strained InAsSb/InAs MQW active region operated up to 210 K in pulsed mode with an emission wavelength of 3.8--3.9 {micro}m and a characteristic temperature of 29--40 K. They also present results for both optically pumped and injection lasers with InAsSb/InAsP SLS active regions. The maximum operating temperature of an optically pumped 3.7 {micro}m SLS laser was 240 K. An SLS LED emitted at 4.0 {micro}m with 80 {micro}W of power at 300 K

Origin of the time dependence of wet oxidation of AlGaAs

The time-dependence of the wet oxidation of high-Al-content AlGaAs can be either linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time dependence can be explained by the increased rate of the formation of intermediate As{sub 2}O{sub 3} vs. its reduction to elemental As. A steadily increasing thickness of the As{sub 2}O{sub 3}-containing region at the oxidation front will shift the process from the linear to the parabolic regime. This shift from reaction-rate-limited (linear) to diffusion-limited (parabolic) time dependence is favored by increasing temperature or increasing Al mole fraction

Novel Mid-Infrared Lasers With Compressively Strained InAsSb Active Regions

Mid-infrared lasers grown by MOCVD with AlAsSb claddings and strained InAsSb active regions are reported. A 3.8--3.9 {micro}m injection laser with a pseudomorphic InAsSb multiple quantum well active region lased at 210 K under pulsed operation. A semi-metal layer acts as an internal electron source for the injection laser. An optically pumped laser with an InAsSb/InAsP strained-layer superlattice active region was demonstrated at 3.7 {micro}m, 240 K

The growth and doping of Al(As)Sb by metal-organic chemical vapor deposition

AlSb and AlAs{sub x}Sb{sub 1{minus}x} epitaxial films grown by metal-organic chemical vapor deposition were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500 C and 76 torr using trimethylamine or ethyldimethylamine alane and triethylantimony. The authors examined the growth of AlAsSb using temperature of 500 to 600 C, pressures of 65 to 630 torr, V/III ratios of 1--17, and growth rates of 0.3 to 2.7 {micro}m/hour in a horizontal quartz reactor. SIMS showed C and O levels below 2 {times} 10{sup 18} cm{sup {minus}3} and 6 {times} 10{sup 18} cm{sup {minus}3} respectively for undoped AlSb. Similar levels of O were found in AlAs{sub 0.16}Sb{sub 0.84} films but C levels were an order of magnitude less in undoped and Sn-doped AlAs{sub 0.16}Sb{sub 0.84} films. Hall measurements of AlAs{sub 0.16}Sb{sub 0.84} showed hole concentrations between 1 {times} 10{sup 17} cm{sup {minus}3} to 5 {times} 10{sup 18} cm{sup {minus}3} for Zn-doped material and electron concentrations in the low to mid 10{sup 18} cm{sup {minus}3} for Sn-doped material. They have grown pseudomorphic InAs/InAsSb quantum well active regions on AlAsSb cladding layers. Photoluminescence of these layers has been observed up to 300 K