Zhanping Zhu

Using photoluminescence as optimization criterion to achieve high-quality InGaAs/AlGaAs pHEMT structure

The single delta -doped InGaAs/AlGaAs pseudomorphic HEMT structure materials were grown by molecular beam epitaxy. The photoluminescence spectra of the materials were studied. There are two peaks in the photoluminescence spectra of the materials, corresponding to two sub energy levels of InGaAs quantum well. The ratio of the two peaks intensity was used as criterion to optimize the layer structures of the materials. The material with optimized layer ;tructures exhibits the 77 It mobility and two-dimensional electron gas density of 16 500 cm(2)/Vs and 2.58 x 10(12) cm(-2) respectively, and the 300 K mobility and two-dimensional electron gas density of 6800 cm(2)/Vs and 2.55 x 10(12) cm(-2) respectively. The pseudomorphic HEMT devices with gate length of 0.2 mum were fabricated using this material. The maximum transconductance of 650 mS/mm and the cut-off frequency of 81 GHz were achieved

The keys to get high transconductance of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs devices

Abstract There are two key points to get high transconductance of pseudomorphic HEMTS (pHEMTs) devices. From the point view of materials, the transfer efficiency of the electrons from the δ-doped AlGaAs layer to the InGaAs channel must be high. From the point view of device processing, the gate recess depth must be carefully controlled. In the present work, AlGaAs/InGaAs/GaAs pHEMTs structures were grown by molecular beam epitaxy. Layer structures of the pHEMTs were optimized to get high transfer efficiency of the electrons. Gate recess depth was also optimized. A 0.2 μm pHEMT was fabricated on the materials with optimized layer structure using the optimized gate recess depth. The maximum transconductance of 650 mS/mm and the cut-off frequency of 81 GHz were achieved.

Photoluminescence of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs with different thickness of spacer layer

The photoluminescence spectra of the single delta -doped AlGaAs/InGaAs/GaAs pseudomorphic HEMTs with different thickness of spacer layer were studied. There are two peaks in the PL spectra of the structure corresponding to two sub-energy levels of the InGaAs quantum well. It was found that the photoluminescence intensity ratio of the two peaks changes with the spacer thickness of the pseudomorphic HEMTs. The reasons were discussed. The possible use of this phenomenon in optimization of pseudomorphic HEMTs was also proposed

High-quality metamorphic HEMT grown on GaAs substrates by MBE

Metamorphic high electron mobility transistor (M-HEMT) structures have been grown on GaAs substrates by molecular beam epitaxy (MBE). Linearly graded and the step-graded InGaAs and InAlAs buffet layers hal e been compared, and TEM, PL and low-temperature Hall have been used to analyze the properties of the buffer layers and the M-HEMT structure. For a single-delta-doped M-HEMT structure with an In0.53Ga0.47As channel layer and a 0.8 mum step-graded InAlAs buffer layer, room-temperature mobility of 9000 cm(2)/V s and a sheet electron density as high as 3.6 x 10(12)/cm(2) are obtained. These results are nearly equivalent to those obtained for the same structure grown on an InP substrate. A basic M-HEMT device with 1 mum gate was fabricated, and g(m) is larger than 400 mS/mm

Silicon doping induced increment of quantum dot density

Low-indium-content self-assembled InGaAs/GaAs quantum dots (SAQD) were grown using solid-source molecular beam epitaxy (MBE) and investigated by atomic force microscopy and photoluminescence (PL) spectroscopy. Silicon, which was doped at different quantum dot (QD) growth stages, markedly increased the density of QD. We obtained high density In0.35Ga0.65As/GaAs(001) quantum dots of 10(11)/cm(2) at a growth temperature of 520degreesC. PL spectra and distribution statistics show the high quality and uniformity of our silicon-doped samples. The density increment can be explained using the lattice-hardening mechanism due to silicon doping.

Influences of organic–inorganic interfacial properties on the performance of a hybrid near-infrared optical upconverter

In this article, we explored in detail the influences of organic–inorganic interfacial properties on the performance of a hybrid near-infrared optical upconverter, mainly the leakage current and brightness. The upconverter that can convert input near-infrared to visible light was fabricated by directly integrating an organic light emitting diode (OLED) with an In0.12Ga0.88As/GaAs multi-quantum wells (MQWs) photodetector (PD). MoO3 doped perylene-3,4,9,10-tetra carboxylic dianhydride (PTCDA) was inserted between the PD and OLED as an interfacial connection layer. The possible interaction mechanism of the PTCDA molecule on the GaAs surface such as π electron cloud spreading or Ga–O–C bonds model was suggested and verified to explain the excellent hole injection property at the GaAs/MoO3:PTCDA interface. In addition, choosing an effective interface passivation layer was proven to retain leakage current markedly.

Growth and Characterization of InSb Thin Films on GaAs (001) without Any Buffer Layers by MBE

We report the growth of InSb layers directly on GaAs (001) substrates without any buffer layers by molecular beam epitaxy (MBE). Influences of growth temperature and V/III flux ratios on the crystal quality, the surface morphology and the electrical properties of InSb thin films are investigated. The InSb samples with room-temperature mobility of 44600 cm/Vs are grown under optimized growth conditions. The effect of defects in InSb epitaxial on the electrical properties is researched, and we infer that the formation of In vacancy (V) and Sb anti-site (Sb defects is the main reason for concentrations changing with growth temperature and Sb/In flux ratios. The mobility of the InSb sample as a function of temperature ranging from 90 K to 360 K is demonstrated and the dislocation scattering mechanism and phonon scattering mechanism are discussed.

Optimization of InGaAs quantum dots for optoelectronic applications

Quantum dot infrared photodetectors (QDIP) are at the center of research interest nowadays. However, the real QDIP is inferior to those predicted in theory, in which the dot density is much higher than those reported. Through optimizing the growth conditions, we realized the control of high-density quantum dot growth. This will be very useful for future QDIP development.

808 nm high-power laser grown by MBE through the control of Be diffusion and use of superlattice

808 nm high-power laser diodes are gown by MBE. In the laser structure, the combination of Si-doped GRIN (graded-index) region adjacent to n-AlGaAs cladding layer with reduced Be doping concentration near the active region has been used to diminish Be diffusion and oxygen incorporation. As compared with the laser structure which has undoped GRIN region and uniform doping concentration for Si and Be, respectively, in the cladding layers, the slope efficiency has increased by about 8%. Typical threshold current density of 300 A/cm(2) and the minimum threshold current density of 220 A/cm(2) for lasers with 500 mu m cavity length are obtained. A high slope efficiency of 1.3 W/A for coated lasers with 1000 mu m cavity length is also demonstrated, Recorded CW output power at room temperature has reached 2.3 W.

High-power GRIN-SCH lasers with low-threshold-current density and high efficiency

In this letter, we report the MBE growth of GRIN-SCH ALGaAs single quantum well lasers. In order to obtain high quality laser materials, superlattice among GaAs buffer and n-AlGaAs cladding layer was incorporated. Reduced Be dopant concentration in the p-AlGaAs cladding layer near the GRIN region was adopted, which is believed to be benefit to the control of p-n junction places and reduction of the oxygen incorporation. High power broad-area lasers were fabricated. The typical threshold current density is 300A/cm2 and the minimum threshold current density is 220A/cm2 for the 500 micrometers cavity length lasers. High slope efficiency of 1.3W/A for 1000 micrometers cavity length lasers was obtained, recorded CW output power at room temperature has reached 2.3W. The measured characteristics temperature T(subscript 0