COMMAD 2000 Proceedings. Conference on Optoelectronic and Microelectronic Materials and Devices

Current passing in the forward direction through a GaAs-based heterojunction at liquid helium temperatures exhibits, under a strong magnetic field applied parallel to the junction plane, regular fluctuations. We argue that these fluctuations are associated with the formation of closed Aharonov-Bohm-type orbits encircling misfit dislocations generated at the interface in which the current carriers are temporarily trapped.

We report on widegap II-VI compound short wavelength optical modulators of ZnSe/ZnMgSSe asymmetric coupled quantum wells (ACQWs). Effective mass approximated calculations have shown that ZnSe(50/spl Aring/)-ZnMgSSe(30/spl Aring/)-ZnSe(20/spl Aring/) ACQW exhibits weak Stark effect region (<40 kV/cm) and strong Stark effect region (>40 kV/cm). These simulations are experimentally confirmed by a p-i-n structure ACQW modulator grown by molecular beam epitaxy (MBE). The present device exhibits a low reverse bias operation (/spl sim/8 V) with modulation ratio(T/sub on//T/sub off/) of 1.08 at room temperature.

Molybdenum trioxide - tungsten trioxide (MoO/sub 3/-WO/sub 3/) binary metal oxide thin films have been prepared by the sol-gel process. The films were deposited using the spin coating technique onto alumina substrates with interdigital electrodes and single crystal silicon substrates for electrical and micro characterization. Scanning Electron Microscopy (SEM) showed MoO/sub 3/-WO/sub 3/ film morphology composed of MoO/sub 3/ needle like grains and WO/sub 3/ spherical grains when annealed at 450/spl deg/C. The films exhibited selective gas sensing characteristics at an operating temperature of 300/spl deg/C towards nitrogen dioxide (NO/sub 2/).

Impurity free vacancy disordering (IFVD) is induced in both GaAs/AlGaAs and InGaAs/AlGaAs QWs using undoped, Ga-doped and P-doped spin-on glass encapsulant layers. IFVD has been studied for different annealing and pre-baking temperatures, using low temperature photoluminescence (PL). The P-doped and undoped silica layers behave similarly in promoting IFVD, inducing large energy shifts. The Ga-doped silica layer suppresses IFVD, which is explained by the reduction of Ga outdiffusion from the QW structure into the oxide layer.

From the theoretical calculations on bound-to-continuum transitions in III-V compound n-type square well QWIPs based on the eight band k.p model incorporated with the envelope function approximation, it was found that a small response to TE mode infrared field excitation is possible. The role of the interband transition momentum matrix element P=-i within different regions of the QWIP is investigated, using two different material systems, namely GaAs/AlGaAs and InGaAs/GaAs. An asymmetric step well QWIP based on the study has been designed to improve the response to TE polarized excitation. The experimental measurements on the responsivity of the asymmetric QWIP are also presented.

We describe total energy calculations based on density functional theory of defect complexes in ZnSe containing nitrogen. As a main result, a complex of a nitrogen interstitial with a selenium vacancy, which results from a movement of a nitrogen atom from the substitutional to the interstitial site, is much more stable than the nitrogen acceptor. We show that the typical signatures of such a complex can be detected in optical degradation experiments on stacking-fault-free ZnSe based laser diodes. The degradation process can thus be understood as a decay of the thermodynamically unstable nitrogen acceptor. From theoretical considerations, this process is predicted to be influencable by strain engineering and the admixture of tellurium to the p-layer. On a prototype device we demonstrate that a combination of these measures in fact leads to a drastic lifetime increase of devices.

The effects of wet anisotropic etching of [100] silicon were studied with mask edges aligned at 45/spl deg/ to the primary wafer. Samples were etched in aqueous KOH solution with the addition of isopropyl alcohol (IPA). The addition of IPA caused a change from the formation of vertical {100} walls to sloping {110} walls only for solutions below a critical concentration and temperature. The dependence on concentration was then applied to produce a new multilayer structure with {110} walls fabricated on top of {100} walls.

Antireflection (AR) coated laser diodes are very much desirable in various external cavity semiconductor laser configurations. Present work describes a simple method of silicon nitride AR coatings on infrared semiconductor lasers. Silicon nitride AR coatings were done on InAlGaAs semiconductor laser diodes emitting at 980nm by reactive sputtering. A residual reflectivity of 10/sup -2/ was achieved which is acceptable for most practical applications. Comparison of experimental observations with the calculations of AR coating thickness and film refractive index shows good qualitative agreement. The AR coated laser diode was tested for its performance by operating it in an external cavity.

The effect of high gate-to-drain transverse field stressing at cryogenic temperature is characterized through gate-to-drain capacitance measurement. A larger degradation effect is observed at low temperature measurement because the effect of Coulomb scattering by interface charge on mobility degradation is more significant and carrier concentration is more sensitive to surface potential variation. Also, more acceptor states are ionized causing increase in interface charges. For low stressing temperature, more trapped holes and interface states are created. These holes trapping are due to shallow-level trap centers where the captured holes will thermally re-emit as the device is warmed to room temperature.

Hành vi mới của các diode laser (LDs) và diode siêu phát sáng (SLDs) được tạo ra trên các substrat với giếng lượng tử không đồng nhất đã được phát hiện. Các diode laser/ diode siêu phát sáng với giếng lượng tử không đồng nhất đã được thiết kế, chế tạo và đo đạc. Sự phân bố không đồng nhất của các hạt mang điện bên trong nhiều giếng lượng tử cũng đã được xác nhận thực nghiệm. Các đặc điểm đo được cũng cho thấy rằng electron, thay vì lỗ trống, là hạt mang điện chi phối việc phân bố hạt mang điện. Chuỗi giếng lượng tử không đồng nhất cũng đã cho thấy ảnh hưởng đáng kể đến các đặc điểm của thiết bị, cho thấy sự phân bố hạt mang điện rất khác nhau trong mỗi chuỗi.