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The active photo-excited carrier has been identified in reverse biased quantum dot resonant tunneling diode (QDRTD) for light detection. The QD is embedded on the AlAs/GaAs/AlAs double barrier part of the material structure and is found with strong charge memory effect. The QD is charged with electrons in forward bias and the charge storage of QD is maintained well in reverse bias until the voltage of QD resonant tunneling peak. With this charge memory effect, the photo-excited holes are charged into QDs in forward bias and still influence the reverse bias behavior of QDRTD at dark. Compared to the illuminated QDRTD in reverse bias, the active photo-excited carrier of reverse biased QDRTD is unambiguously identified as photo-excited holes. The potential profile of QDRTD structure is also calculated and the potential near charged QDs is found greatly pushed up above GaAs E C . This may explain the trapping of photo-excited hole by QD for QDRTD in reverse bias.

For reducing turn-on voltage of GaAs-based HBT, Al 0.25 Ga 0.75 As/GaAs 0.89 Sb 0.11 /GaAs DHBTs on GaAs (001) is successfully grown by solid-source molecular beam epitaxy (SSMBE) with a GaAs decomposition source, no misfit dislocation in the base layer was found by observation of SEM. It suggests that GaAsSb base layer is fully strained. Device with 75×75μm 2 emitter mesa area is fabricated using this structure and yielded an excellent performance with high current gain of 30 at the collector current density of 2×10 3 A/cm 2 and low turn-on voltage of 0.8V. Due to the smaller band gap of the GaAsSb base layer, GaAsSb is useful material for reducing turn-on voltage of GaAs-based HBTs.

Planar punch through heterojunction phototransistors with a novel emitter control electrode and ion- implanted isolation (CE-PTHPT) are investigated. The phototransistors have a working voltage of 3-10V and high sensitivity at low input power. The base of the transistor is completely depleted under operating condition. Base current is zero. The CE-PTHPT has an increased speed and a decreased noise. The novel CE-PTHPT has been fabricated in this paper. The optical gain of GaAlAs/GaAs CE-PTHPT for the incident light power 1.3 and 43nw with the wavelength of 0.8 mu m reached 1260 and 8108. The input noise current calculated is 5.46 x 10(-16) A/H-z(1/2). For polysilicon emitter CE-PTHPT, the optical gain is 3083 at the input power of 0.174 mu w. The optical gain of InGaAs/InP CE-PTHPT reaches 350 for an incident power of 0.3 mu w at the wavelength of 1.55 mu m. The CE-PTHPT detectors is promising as photo detectors for optical fiber communication system.

Micro-photoluminescence ((mu) -PL) experiments have been carried out on the cleaved facet of quantum well infrared photodetector to extract multiple quantum well signal. Some structures and peak response wavelength have been estimated by a numerical calculation based on the square well model. Thus, a relationship between PL spectrum and parameters was built.

The GaN growth and Si-doped GaN are studied in this work. By means of x-ray diffraction and photoluminescence (PL) measurements we found that the GaN sample directly grown on GaAs substrate is pure cubic phase and that grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers. The PL properties of Si-doped cubic GaN with different carrier concentrations were investigated at room temperature. It was found that when the carrier concentration is increased from 5 X 1015 to 2 X 1018cm-3, the PL peak shifted towards low energy, from 3.246 to 3.227 eV, and the PL linewidth increased from 77.1 to 121 meV. The PL peak shift is explained by the bandgap narrowing effect due to the high doping concentration. The PL linewidth includes two parts: one is doping concentration-independent, which is caused by the imperfection of samples and phonon scattering; the other is doping concentration-dependent. We assign the second part to the broadening by the microscopic fluctuation of the doping concentration. The experimental measurements are in good agreement with the model.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed a new MBE growth technique by using low-temperature-Si (LT-Si) or LT-GeSi buffer layers. Even ifthe Ge fraction up to 90%, the total thickness of fully relaxed GeSi1 buffers can be reduced to 1 .7 tm with dislocationdensity lower than 5x 106 cm2. The roughness is no more than 6 nm. According to the analysis of X-ray diffraction, the crystal quality of the top layer is very good, and the strain relaxation is quite inhomogeneous from the beginning of relaxation. By using high resolution cross section TEM, we observed that stacking faults are induced and form the misfitdislocations in the interface of GeSi/LT-Si. We propose that the formation of the stacking faults is due to the aggregation ofthe large amount ofthe vacant defects in the LT-Si layer.Keywords: dislocation, stacking faults, vacancy, strain relax, silicon, germanium 1. INTRODUCTION Some GeSi/Si heterostructures devices require relaxed GeSi buffers to serve as virtual substrates. Unfortunately, 4% oflattice mismatch often results in high threading dislocation (TD) density even up to 10' cm2. [1][2] Therefore, to decrease theTD density has attracted great attention. Among various techniques used, the compositionally graded buffer seems to be avery useful one by which the TD density can be reduced to as low as I 06 cm2. E3][4] However, such buffers are usually verythick and the surface corrugation is serious with an amplitude of up to 15-2Onm, and the Ge composition can not be higherthan 0.5 under the TDs density less than iO cm2.We have developed a new MBE growth technique, by which, relaxed, thin, and uniform GeSi layer with low TDs density isgrown on low-temperature-Si (LT-Si) or LT-GeSi buffer layers.

Comparative electroluminescence (EL) and photoluminescence (PL) measurements were performed on Si/Si0.6Ge0.4 self-assembly quantum dots (QDs) structures. The samples were grown pseudomorphically by molecular beam epitaxy, and PIN diodes for electroluminescence were fabricated. Assisted TEM pictures shows the SiGe self-assembly QDs are platelike. And it showed that the diameters of QDs are in range from 40nm to 140nm with the most in 120nm. Both EL and PL has a wide luminescence peak due to wide distribution of QDs dimensions. At low temperature (T=14K), EL peak has a red shift compared to the corresponding PL peak. Its full-width at half-maximum (FWHM) is about 97meV, a little smaller than that of corresponding PL peak. The reasons of position and FWHM changes of EL peak from QDs have been discussed.

In this paper, the compatibility of P+-GexSi1-x/p-Si heterojunction internal photoemission IR detector (HIP IRD) with its CMOS readout circuit is analyzed with a feasible approach presented. The experimental chip in which P+-GexSi1-x/p-Si HIP IRD and its NMOS readout switch are monolithically integrated has been fabricated with a 3 micrometers NMOS technology. The MBE grown detector without the dielectric cavity and anti-reflecting layer has a blackbody detectivity D*(500, 1000, 1) of 1.1 X 109cmHz1/2/W at the temperature of 77K. The selective readout of the output signals of the detectors through the NMOS readout switch at 77K has been achieved. Therefore, the feasibility of fabricating monolithically integrated P+-GexSi1-x/p-Si HIP IR focal plane array with NMOS readout circuit was demonstrated preliminarily.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A long-wavelength 128 by 1 GaAs/AlGaAs multiple quantum wells (MQWs) infrared detector (IRD) array is presented. A good photo-current responsibility Rp equals 2.02 X 106V/W is obtained with the cut-off wavelength being (lambda) c equals 8.6 micrometer and as a result, we obtain a good remanent heat image of a room-temperature subject.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, we present a new electrode structure for P-GeSii/p-Si heterojunction internal photoemission (HIP) long-wavelength infrared detector (LWIRD). The advantages of this structure have been verified by experimental results. The electrical and photoresponse characteristics of the detector with 1 OOnm-thick Ge03Si0.7 layer at 77K are reported. In addition, a new analytic quantum efficiency (QE) model for P-GeSi1Ip-Si HIP LWIRD is builtbased on modification of old model. Comparing with old models, it is characterized in that the impact of carrierstransporting on quantum efficiency is considered. It is shown that this model is more consistent with actuality thanold model through the comparison between the theoretical results and experimental results. The optimal thicknessof GeSii. layer can be estimated by this model and the result is also agree with experiment.Keywords: long-wavelength infrared detectors (LWIRD ), Germaniumsilicon alloy, quantum efficiency (QE) 1. INTRODUCTIONMore attention has been paid to P-GeSi1/p-Si hoterojunction internal photoemission (HIP) long-wavelengthinfrared detector (LWIRD) in recent years because of its advantages such as easily to be monolithically integratedwith CCD or CMOS readout circuitry, relatively higher quantum efficiency (QE) than silicide Schottky-barrierdetectors, wide range of photoresponse including 35.tm and 8.-..l4.tm, adjustable cutoff wavelength through

Using 45 degree(s) geometry or grating for optical coupling, three kinds of GaAs/AlxGa1-xAs multiquantum well (MQW) photodetectors having different response range, i.e., 7.50 - 8.85, 8.20 - 9.80, and 9.60 - 11.40 micrometers , have been fabricated and evaluated. High responsivity Rp > 1 X 105 V/W, high quantum efficiency (eta) > 14%, and high detectivity D(lambda )* > 3 X 1010 cmHz1/2/W, were achieved at T equals 77 K.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.