InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength infrared detectors

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength (3-5 mum) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3-5.3 mum infrared atmospheric transmission window. The blackbody detectivity (D-bb*) of the detectors reaches to about 1.0x10(10) cm Hz(1/2)/W at 77 K under bias of +/-7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. (C) 2001 American Institute of Physics.

Properties and turning of intraband optical absorption in InxGa1-xAs/GaAs self-assembled quantum dot superlattice

We investigated properties of intraband absorption in In-x Ga1-xAs quantum dots (QDs) superlattice. Energy levels in conduction band in QDs were calculated for a cone-shaped quantum dot associated with coupling between QDs in the framework of the effective-mass envelope-function theory. Theoretical results demonstrated that energy levels in conduction band were greatly affected by the vertical coupling between quantum dots, which can be used to modify transition wavelength by adjusting the space layer thickness. Intraband transition is really sensitive to normal incidence and the absorption peak intensity is dependent on the polarization. A satisfying agreement is found between theoretical and experimental values. This result opens up prospects for the fabrication of QDs infrared detectors, which work at atmospheric windows.

Using Fourier transform infrared grazing incidence reflectivity to study local vibrational modes in GaN

Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission methods have been used to study GaN films grown on alpha-Al2O3 (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. The results show that in the frequency range from 400 to 3500 cm(-1) the signal-to-noise ratio of the FTIR grazing incidence measurement is far higher than that of the FTIR transmission measurement. Some new vibrational structures appearing in the former measurement have been discussed. The features around 1460 and 1300 cm(-1) are tentatively assigned to scissoring and wagging local vibrational modes of CH2 in GaN, respectively. (C) 1999 American Institute of Physics. [S0021-8979(99)06509-3].

Intraband absorption in the 8-12 mu m band from Si-doped vertically aligned InGaAs/GaAs quantum-dot superlattice

Normal-incident infrared absorption in the 8-12-mu m-atmospheric spectral window in the InGaAs/GaAs quantum-dot superlattice is observed. Using cross-sectional transmission electron microscopy, we find that the InGaAs quantum dots are perfectly vertically aligned in the growth direction (100). Under the normal incident radiation, a distinct absorption peaked at 9.9 mu m is observed. This work indicates the potential of this quantum-dot superlattice structure for use as normal-incident infrared imaging focal arrays application without fabricating grating structures. (C) 1998 American Institute of Physics. [S0003-6951(98)01151-6].

NEW METHOD FOR ACQUIRING A HIGH-RESOLUTION ATMOSPHERIC RAYLEIGH-MIE SPECTRUM

A new method using an atomic-resonance filter and deconvolution techniques has been developed to acquire high-resolution spectra of atmospheric Rayleigh-Mie scattering. In the deconvolution process, the difficulty of the undetermined division 0/0 is overcome by a fitting method. Preliminary laboratory experimental results on 90-deg scattering show that with a signal-to-noise ratio of 20, the scattered Rayleigh-Mie spectrum may be retrieved in agreement with the theoretical analysis.

OPTICAL AND STRUCTURAL-PROPERTIES OF AP-MOVPE GAINP/GAAS HETEROSTRUCTURES

Lattice matched GaInP/GaAs heterostructures were grown by atmospheric pressure-metal organic vapor phase epitaxy (AP-MOVPE). Compositional intermixing of As/P and Ga/In near the heterointerfaces was studied by photoluminescence (PL) spectroscopy. Indium segregation, memory effect of In into GaAs and the carry-over of As in the GaInP layer during the growth process were considered as three major factors giving rise to the anomalous emissions in the PL spectra. Both thermal annealing and zinc doping strongly enhanced the compositional interdiffusion near the heterointerfaces.

Effects of heavy and light hole mixing in quantum well physics