Defects in GaN films grown on Si(111) substrates by metal-organic chemical vapour deposition

We report the transmission-electron microscopy study of the defects in wurtzitic GaN films grown on Si(111) substrates with AIN buffer layers by the metal-organic chemical vapour deposition method. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations passing through the MQW. No evident reduction of the edge dislocations density by the MQW was observed. It was found that dislocations with screw component can be located at the boundaries of sub-grains slightly in-plane misoriented.

Microstructure of GaN films grown on Si(111) substrates by metalorganic chemical vapor deposition

We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(I I I) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed. (C) 2003 Elsevier B.V. All rights reserved.

Magnetic-field-induced nonthermal occupation of higher subbands in a three-barrier tunneling structure

When injected electrons in a quantum well first experience an intersubband relaxation process before their escaping by tunneling through a double-barrier structure behind, the magnetic suppression of intersubband LO or LA phonon scattering can give rise to a noticeable nonthermal occupation in higher-lying subbands. That is clearly verified by the relative intensity ratio of the interband photoluminescence spectra for E-2-HH1 and E-1-HH1 transitions. The observed phenomenon may provide an effective method for controlling intersubband scattering rate, a central issue in so-called quantum cascade lasers, and facilitating the population inversion between subbands in quantum wells.

Resonant tunneling of holes in GaMnAs-related double- barrier structures

Using the multiband quantum transmitting boundary method (MQTBM), hole resonant tunneling through AlGaAs/GaMnAs junctions is investigated theoretically. Because of band-edge splitting in the DMS layer, the current for holes with different spins are tuned in resonance at different biases. The bound levels of the "light" hole in the quantum well region turned out to be dominant in the tunneling channel for both "heavy" and "light" holes. The resonant tunneling structure can be used as a spin filter for holes for adjusting the Fermi energy and the thickness of the junctions.

Growth temperature effect on the optical and material properties of AlxInyGa1-x-yN epilayers grown by MOCVD

AlxInyGa1-x-yN epilayers have been grown by metalorganic chemical vapor deposition (MOCVD) at different temperatures from 800 to 870degreesC. The incorporation of indium is found to increase with decreasing growth temperature, while the incorporation of Al remains nearly constant. The optical properties of the samples have been investigated by photoluminescence (PL) and time-resolved photoluminescence (TRPL) at different temperatures. The results show that the sample grown at 820 C exhibits the best optical quality for its large PL intensity and the absence of the yellow luminescence. Furthermore the temperature-dependent PL and TRPL of the sample reveals its less exciton localization effect caused by alloy fluctuations. In the scanning electron microscopy measurement, much uniform surface morphology is found for the sample grown at 820degreesC, in good agreement with the PL results, The improvement of AlxInyGa1-x-yN quality is well correlated with the incorporation of indium into AlGaN and the possible mechanism is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

Storage of photoexcited electron-hole pairs in an AlAs/GaAs heterostructure created by electron transfer in real and kappa spaces

The storage of photoexcited electron-hole pairs is experimentally carried out and theoretically realized by transferring electrons in both real and k spaces through resonant Gamma - X in an AlAs/GaAs heterostructure. This is proven by the peculiar capacitance jump and hysteresis in the measured capacitance-voltage curves. Our structure may be used as a photonic memory cell with a long storage time and a fast retrieval of photons as well.

The effects of concomitant In and N incorporation on the photoluminescence of GaInNAs

We investigated the effects of concomitant In- and N-incorporation on the photoluminescence (PL) of GaInNAs grown by molecular beam epitaxy. In comparison with the N-free GaInAs epilayer, the PL spectra of the GaInNAs epilayer exhibit an anomalous S-shape temperature dependence of dominant luminescence peak. Through further careful inspection, two PL peaks are clearly discerned and are associated with the interband excitonic recombinations and excitons bound to N-induced isoelectronic impurity states, respectively. By comparing the PL spectra of GaInNAs/ GaAs quantum wells (QWs) with those of In-free GaNAs/GaAs QWs grown under similar conditions, it is found that the concomitant In- and N-incorporation reduces the density of impurities and has an effect to improve the intrinsic optical transition of GaInNAs, but also enhance the N-induced clustering effects. At last, we found that rapid thermal annealing can significantly reduce the density of N-induced impurities. (C) 2002 Elsevier Science B.V. All rights reserved.

SiGe/Si resonant-cavity-enhanced photodetectors for 1.3 mu m operation fabricated using wafer bonding techniques

A SiGe/Si multiple-quantum-well resonant-cavity-enhanced (RCE) photodetector for 1.3 mum operation was fabricated using bonding reflector process. A full width at half maximum (FWHM) of 6 nm and a quantum efficiency of 4.2% at 1314 nm were obtained. Compared to our previously reported SiGe RCE photodetectors fabricated on separation-by-implanted-oxygen wafer, the mirrors in the device can be more easily fabricated and the device can be further optimized. The FWHM is expected to be less than 1 nm and the detector is fit for density wavelength division multiplexing applications. (C) 2002 American Institute of Physics.

Tuning of exciton-photon coupling in a planar semiconductor microcavity by applying hydrostatic pressure

By means of hydrostatic pressure tuning, we have observed the strong-coupling exciton-polariton mode in a planar microcavity with an InGaAs/GaAs quantum well embedded in it, over a pressure range from 0.37 to 0.41 GPa. The experimental data can be fitted very well to a corresponding theoretical formula with a unique value of the vacuum Rabi splitting equal to 6.0 meV. A comparison between pressure tuning and other tuning methods is made as regards to what extent the intrinsic features of the exciton and cavity will be influenced during the tuning procedure.

Exploration on enhancing innovation capability of functional information materials in China

The present status and future prospects of functional information materials, mainly focusing on semiconductor microstructural materials, are introduced first in this paper. Then a brief discussion how to enhance the academic level and innovation capability of research and development of functional information materials in China are made. Finally the main problems concerning the studies of materials science and technology are analyzed, and possible measures for promoting its development are proposed.

Subband electron properties of highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates

A Shubnikov-de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i=1). Very close mobilities of 5859 and 5827 cm(2)/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95x10(12) cm(-2) due to incomplete transfer of the electrons from the Si delta -doped layer to the well. (C) 2001 American Institute of Physics.

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. (C) 2001 Elsevier Science B.V. All rights reserved.

Si-based resonant-cavity-enhanced photodetector

We report one top-illumination and one bottom-illumination SiGe/Si multiple quantum-well (MQW) resonant-cavity-enhanced (RCE) photodetector fabricated on a separation-by-implanted-oxygen (SIMOX) wafer operating near 1300 nm. The buried oxygen layer in SIMOX is used as a mirror to form a vertical cavity with the silicon dioxide/silicon Bragg reflector deposited on the top surface. A peak responsivity with a reverse bias of 5 V is measured 10.2 mA/W at 1285 nm, a full width at half maximum of 25 nm for the top-illumination RCE photodetector, 19 mA/W at 1305 nm, and a full width at half maximum of 14 nm for the bottom-illumination one. The external quantum efficiency of the bottom-illumination RCE photodetector is up to 2.9% at 1305 nm, with a reverse bias of 25V. The responsivity of the bottom-illumination RCE photodetector is improved by two-fold compared with that of the top-illumination one. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

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 peak's 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. (C) 2001 Elsevier Science B.V. All rights reserved.

Growth and characterization of GaInNAs/GaAs by plasma-assisted molecular beam epitaxy

We have studied the growth of GaInNAs/GaAs quantum well (QW) by molecular beam epitaxy using a DC plasma as the N sourer. The N concentration was independent of the As pressure and the In concentration, but inversely proportional to the growth rate. It was almost independent of T, over the range of 400-500 degreesC, but dropped rapidly when T-g exceeded 500 degreesC. Thermally-activated N surface segregation is considered to account for the strong falloff of the N concentration. As increasing N concentration, the steep absorption edge of the photovoltage spectra of GaInNAs/GaAs QW became gentle, the full-width at half-maximum of the photoluminescence (PL) peal; increased rapidly, and a so-called S-shaped temperature dependence of PL peak energy showed up. All these were attributed to the increasing localized state as N concentration. Ion-induced damage was one of the origins of the localized state. A rapid thermal annealing procedure could effectively remote the localized state. (C) 2001 Elsevier Science D.V. All rights reserved.