Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As

The magnetic properties of the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As are studied within the dynamical cluster approximation. We use the k-dot-p Hamiltonian to describe the electronic structure of GaAs with spin-orbit coupling and strain effects. We show that nonlocal effects are essential for explaining the experimentally observed transition temperature and saturation magnetization. We also demonstrate that the cluster anisotropy is very strong and induces rotational frustration and a cube-edge direction magnetic anisotropy at low temperature. With this, we explain the temperature-driven spin reorientation in this system.Comment: 4 pages, 4 figures; to be published in Phys. Rev. Let

InGaN/GaN disk-in-nanowire white light emitting diodes on (001) silicon

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98666/1/ApplPhysLett_98_193102.pd

Yield and leakage currents of large area lattice matched InP/InGaAs heterostructures

Demonstrating and harnessing electroluminescent cooling at technologically viable cooling powers requires the ability to routinely fabricate large area high quality light-emitting diodes (LEDs). Detailed information on the performance and yield of relevant large area devices is not available, however. Here, we report extensive information on the yield and related large area scaling of InP/InGaAs LEDs and discuss the origin of the failure mechanisms based on lock-in thermographic imaging. The studied LEDs were fabricated as mesa structures of various sizes on epistructures grown at five different facilities specialized in the growth of III-V compound semiconductors. While the smaller mesas generally showed relatively good electrical characteristics and low leakage current densities, some of them also exhibited unusually large leakage current densities. The provided information is critical for the development and design of the optical cooling technologies relying on large area devices.Peer reviewe

GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 μm operation

Hot electron light emission and lasing in semiconductor heterostructure (Hellish) devices are surface emitters the operation of which is based on the longitudinal injection of electrons and holes in the active region. These devices can be designed to be used as vertical cavity surface emitting laser or, as in this study, as a vertical cavity semiconductor optical amplifier (VCSOA). This study investigates the prospects for a Hellish VCSOA based on GaInNAs/GaAs material for operation in the 1.3-μm wavelength range. Hellish VCSOAs have increased functionality, and use undoped distributed Bragg reflectors; and this coupled with direct injection into the active region is expected to yield improvements in the gain and bandwidth. The design of the Hellish VCSOA is based on the transfer matrix method and the optical field distribution within the structure, where the determination of the position of quantum wells is crucial. A full assessment of Hellish VCSOAs has been performed in a device with eleven layers of Ga0.35In0.65N0.02As0.08/GaAs quantum wells (QWs) in the active region. It was characterised through I-V, L-V and by spectral photoluminescence, electroluminescence and electro-photoluminescence as a function of temperature and applied bias. Cavity resonance and gain peak curves have been calculated at different temperatures. Good agreement between experimental and theoretical results has been obtained

Ga0.35In0.65 N0.02As0.08/GaAs bidirectional light-emitting and light-absorbing heterojunction operating at 1.3 μm

The Top-Hat hot electron light emission and lasing in semiconductor heterostructure (HELLISH)-vertical-cavity semiconductor optical amplifier (THH-VCSOA) is a bidirectional light-emitting and light-absorbing heterojunction device. The device contains 11 Ga0.35In0.65 N0.02As0.08/GaAs MQWs in its intrinsic active region which is enclosed between six pairs of AlAs/GaAs top distributed Bragg reflectors (DBRs) and 20.5 pairs of AlAs/GaAs bottom DBR mirrors. The THH-VCSOA is fabricated using a four-contact configuration. The wavelength conversion with amplification is achieved by the appropriate biasing of the absorption and emission regions within the device. Absorption and emission regions may be reversed by changing the polarity of the applied voltage. Emission wavelength is about 1,300 nm and a maximum gain at this wavelength is around 5 dB at T = 300 K

Design and modeling of a transistor vertical-cavity surface-emitting laser

A multiple quantum well (MQW) transistor vertical-cavity surface-emitting laser (T-VCSEL) is designed and numerically modeled. The important physical models and parameters are discussed and validated by modeling a conventional VCSEL and comparing the results with the experiment. The quantum capture/escape process is simulated using the quantum-trap model and shows a significant effect on the electrical output of the T-VCSEL. The parameters extracted from the numerical simulation are imported into the analytic modeling to predict the frequency response and simulate the large-signal modulation up to 40 Gbps