Search

Pseudomorphic four-period GaAs0.978N0.022/GaAs0.78Sb0.22 type-II multi-quantum well structures were grown on (100) GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Photoluminescence (PL) peak energies were obtained from GaAsN/GaAsSb type-II superlattive structures grown by MOVPE.

The performance characteristics of a distributed-feedback quantum-cascade laser exhibiting high-power continuous-wave (CW) operation in a single spectral mode at lambda approximately 4.8-mum and temperatures up to 333 K is measured and modeled. CW output powers of 99 mW at 298 K and 357 mW at 200 K are obtained at current well below the thermal rollover point.

The feasibility of compensating the bulk inversion asymmetry in a [111]-oriented quantum well is investigated. A detailed numerical study of the spin splitting in a suitable InAlAs/InGaAs/InP quantum well grown on a [111] InP substrate is discussed.

An optical parametric oscillator is tuned to the resonance wavelength of the etalon in an optical pumping injection cavity (OPIC) laser with a type-II 'W' active region, thereby minimizing the threshold pump intensity and maximizing the output slope efficiency. The energy conversion efficiency is found to decrease by over a factor of 100 when the pump wavelength is tuned from the resonance condition (1822 nm at 300 K) to only slightly off resonance.

The negative luminescent properties of HgCdTe photodiodes having peak emission at a wavelength of 7.6 micrometer, as a function of temperature and applied bias is investigated. The findings show that the small currents needed to drive the diodes, together with their long-wavelength luminescence, make them suitable for a range of device applications.

Research describing the band parameters for wurtzite and zinc blende compound semiconductors with their ternary and quaternary alloys is presented. Complete parameter sets are given for all the III-V compound materials.

Self consistent beam propagation was used to calculate far field emissions of mid infrared angled grating distributed feedback lasers.

The spectral characteristics, temperature thresholds, peak output power, external power conversion efficiencies, internal losses and Auger efficiencies, of three optically pumped type-II quantum-well 'W' lasers, emitting wavelengths at the 5.4 to 7.3 micron range, have been studied. Among the findings are that maximum operating temperatures range between 220 to 290K, while the peak output can go as high as 1.6 W/facet at 80 K. Internal losses have been found to be moderate when T is 80 K but increase at higher temperatures.

Optically pumped type-II antimonide quantum wells in a magnetic field were used in developing spin-polarized intersubband lasers. These lasers perform well, with wavelengths into the 60 to 100 micron range. Shorter wavelength operation is also possible when a 2-micron pump laser is used and by utilizing the large conduction band offset between InAs and AlSb. Optical pumping is very effective when the electrons are pumped directly into the upper lasing Landau level or into another higher energy level.

Research was conducted to examine three critical growth parameters that affect the properties of type-II infrared laser structures. It was observed that the optimum growth temperature was relatively narrow, at most from 400 to 450 degrees C. Results also demonstrate that laser structures with InSb-like interfacial bonds that are grown using a cracked Sb source reveal better photoluminescence efficiency.

A study was conducted to analyze relaxation kinetics in a quantum cascade intersubband laser. A kinetic model was utilized to consider the intra and intersubband electron-LO-phonon relaxation supporting characteristic times. Experimental results indicated that step-like distributions in the lasing bands and number of nonequilibrium phonons in the active area were self-consistent from kinetic and energy balance equations.

An improved quantitative mobility spectrum analysis (i-QMSA) approach is presented that is based on a new technique that optimizes the fit to the conductivity tensor components and their slopes by adjusting the mobility spectra such that the greatest error reduction is reduced. Compared to the original quantitative spectrum analysis, i-QMSA features a number of innovations that include the reduction of errors between sigma (sub xx) and sigma (sub xy) at each pseudodata point and of errors in the slopes and magnitudes of sigma (sub xx) and sigma (sub xy).

A study was conducted to characterize the design of optically and electrically pumped vertical-cavity surface-emitting lasers (VCSEL) emitting at mid-ir wavelengths using HgTe/Hg(sub 1-x)Cd(sub x)Te active regions. Results suggested the feasibility of operating VCSEL at wavelengths of 4.5 mu-m. Findings also indicated that liquid-nitrogen temperatures could be realized for both optical and electrical pumping at cw or quasi-cw operations.

Research was conducted to study internal losses in optically pumped type-II lasers with InAs/GaSb/Ga(sub 1-x)InxSb/GaSb superlattice active regions. The superlattice lasers produced maximum peak output powers of up to 6.5 W per facet at 100 K and 3.5 per face at 180 K. Temperature-dependent intervalence absorption computations indicated that losses of the magnitude can easily occur if one does not avoid resonances in all regions of the Brillouin zone.

The magnetic-field-dependence boundary-roughness scattering in narrow quantum wires was examined via a two-dimensional finite-difference time-domain model from wave-packet propagation. The results obtained were then compared with predictions of the first-order Born approximation. Both were shown to be in good agreement for single wires, for the case of short disorder correlation length and negligible intersubband scattering. However, the Born approximation notably overestimates the relaxation time when the scattering processes dominate.

Analysis of second-harmonic conversion efficiency achievable from semiconductor intersubband devices using asymmetric stepped and double quantum wells reveals the existence of fundamental limits that constrain the increase of conversion efficiency over 100%. Connecting an optically-inactive momentum-space reservoir to the subband system overcomes the limitations. The reservoir shunts intersubband relaxation and prolongs saturation by refilling the depleted subband states with reservoir electrons.

A modulation mechanism, which encompassed the Stark effect, simulated tau-L transitions at normal incidence in AlSb/InAs/GaSb/AlSb quantum wells that were stepped asymmetrically. This device absorbed normal-incident light when the tau electrons moved toward the L valleys to form intersubband transitions during tau-L crossover. The two deep wells were localized differently in the quantum well whose structure exhibited peculiar band alignments.

Ionized impurity scattering and anisotropic screening are examined in multiple quantum wells and semiconductor superlattices. In semiconductor superlattices, the rate of transition, scattering potentials which are screened anisotropically and free carrier mobility of ionized impurities are measured. The results and the existing data for setback-modulation-doped and modulation doped HgTe-CdTe superlattices are compared.

The stark shifts of the intersubband transition energy are increased by a new type of optical modulator using two-step Ga1-xAlxSb/Ga1-yAlySb/Ga1-zAlzSb L-valley quantum wells. The stark shifts are increased to obtain large absorption spectral changes with applied bias. This new structure intrinsically absorbs the normal incidence light as the effective-mass anisotropy of electrons in the L-valleys and the tilted growth direction with respect to the valleys. For high speed optoelectronic devices, this structure is useful since the incident light is absorbed normally.

Auger recombination carrier lifetimes in HgCdTe quantum wires and quantum boxes with band gaps in the two to five micrometer range were investigated. The results showed that the Auger recombination lifetime in a quantum wire was shorter thanthat observed in quantum wells, and the increased state density resulted in decreased wire width. However, there was no Auger recombination observed in a quantum box.

Presents a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III-V semiconductors that have been investigated to date. Main classes; Tabulation of the direct and indirect energy gaps, spin-orbit and crystal-field splittings; Use of the band anticrossing model to parametrize the fundamental band gap and conduction band properties of the dilute nitride materials.

The effect of an additional GaN spacer layer in InAlN/AlN/GaN structures is analyzed by using simulations, electron-microscopy, magnetoconductivity measurements with gated Hall bar samples and with quantitative mobility spectrum analysis. A possible formation mechanism is proposed for the parasitic layer and although the additional unintended layer has beneficial aspects, a strategy is discussed to prevent its occurrence.

The application of the two-dimensional zinc sulfide photonic crystals (PC) for enhancing the performance of the various organic light-emitting diodes (OLED) is discussed. The periodcity of the PC structure is shown to be the main factor affecting the luminance efficiency of the OLED.

A comprehensive absorption and photoluminescence (PL) study of GaNSb bulk materials grown on nearly lattice-matched GaSb substrates are presented. The results have disclosed the effect of nitrogen incorporation on the fundament mental bandgap and on the character of band edge optical transitions in dilute-nitride GaNSb bulk materials.

A cavity-length study is used for determining the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser with an emission wavelength of 4.05 [micro]m. The strong decrease of the pain per unit current density is due to the dramatic shortening of the Auger lifetime.dauger