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GaN whiskers with nanoscale dimensions are fabricated by photoelectrochemical (PEC) etching in dilute H(sub 3)PO(sub 4) electrolyte. The presence of a dislocation along the central axis of the needles is clearly demonstrated, and the etch pattern is suggested to be related to the growth mechanism for GaN on sapphire.

An analysis of 1.3-Mu-m InGaAsP-InP multiple-quantum-well laser is presented, focusing on output characteristics when changing the p-doping profile. Topics include p-i junction, carrier transport, mechanical calculations of the well properties, and threshold current.

Research was conducted to examine three In(sub 1-x)Ga(sub x)As(sub y)P(sub 1-y)/InP p-i-n multiple quantum well laser structures with various p-doping profiles using contactless electroreflectance and piezoreflectance. The electric field and the amount of p-dopant interdiffusion were analyzed based on the observed Franz-Keldysh oscillations originating in the i-InGaAsP regions. The values of the quantities were in good agreement with high resolution x-ray diffraction calculations.

Electroreflectance (ER), piezoreflectance (PZR) and secondary ion mass spectrometry (SIMS) were employed to analyze two In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) solar cell structures with intrinsic (1)-InP spacers and two InP p-i-n samples. The composition, strain and well width of the MQWs were described by comparing the rich ER/PZR spectra from the MQW regions with an envelope function computation. From the electric fields coming from the i-InP region of the two InP p-i-n control samples, the amount of p-dopant interdiffusion was assessed based on the SIMS data. The results are discussed.

InGaAsP/InP multiple quantum well (MQW) solar cell structures with sequential resonant tunneling between adjacent wells are studied. Results show that the photovoltaic efficiency of the MQW cell has an average 11% increase compared to the control InP samples. The bias voltage and excitation wavelength dependence of photoluminescence and photocurrent for were also determined for the MQW and control samples.

A study was conducted to examine Zn diffusion behavior in capped mesa buried heterostructure lasers. The performance of lasers fabricated with the base cladding layer was also analyzed in the study. The threshold and slope efficiency ratios were represented as a function of the Zn concentration at the heterointerface. Results indicated that the Zn profile in the base epitaxial region was significantly influenced by diffusion during regrowth.

A study was conducted of the relation between the wavelength chirp and carrier temperature in semiconductor lasers. The rate of the temperature increase with current above threshold in MQW InGaAsP lasers was estimated at 0.13 K/mA. The carrier temperature difference between a threshold of 15 mA and a typical operating current of 50 mA was found to be 4.7 K. These findings show the proportionality coefficient between the change of the carrier temperature above threshold and the wavelength chirp.

Multiple quantum well InGaAsP/InP p-i-n laser heterostructures with various barrier thicknesses were studied by photoluminescence (PL) and photocurrent (PC) measurements. The PL spectrum and peak positions obtained were in good agreement with those derived from transfer matrix computations. Comparison of the measured quantum well PC with computed carrier escape rates showed that the photocurrent is controlled by the temperature dependence of the electron escape time.

The effects of interface impurities on the threshold voltage of selectively doped heterostructure field effect transistors are evaluated through experimental and theoretical analysis. Epitaxially grown GaAs semiconductor wafers are treated with carbon and silicon impurities and the structures' voltage characteristics are then studied using a one-dimensional simulation code called SIGMA. Results show that the amount of impurity concentrations affect the transistors' conduction band levels.

Forward voltage of heterostructure transistors is controlled using low energy ion surface layer implantation beneath the gate metal or by changing undoped layer thickness. The undoped layer in the transistor is a GaAs combination. Forward voltage is the gate voltage for a 10 microamperes per micrometer current flow from gate electrode to resistance source and drain electrodes. The source and the drain have a voltage of zero. Molecular beam epitaxy methods are used to form heterostructured wafers.

The presence of carbon on GaAs interface changes the conduction band profile near the interface and depletes charge in the channel resulting to a positive shift of threshold voltage of a depletion mode field effect transistor as the interfacial carbon increases. The magnitude of carrier depletion at the interface between epitaxial GaAs grown by molecular beam epitaxy and a substrate depends on the length of exposure to ozone radiation.

The forward I-V characteristics of InGaN-based light emitting diodes (LEDs) heteroepitaxially grown is dominated by tunneling over a wide range of bias, which is indicated by unrealistic values for the ideality factor. LEDs grown heteroepitaxially and homoepitaxially have displayed a tunneling component that is associated with the heavy hole tunneling via intermediate states.

Importance of heterojunction between the contact and cladding layers in the contact resistance of optoelectronic devices is studied. Incorporation of a quaternary layer, intermediate in composition between these layers provides specific contact resistances that are 60% lower with some R(sub c) values less than 10(super -7) omega cm(super 2).

The temperature dependence of differential gain dG/dn for 1.3-μm InGaAsP-InP FP and DFB lasers with two profiles of p-doping was obtained from RIN measurements within the temperature range of 25°C-65°C. Experiments showed that the change of the active region doping level from 3·1017 cm-3 to 3·1018 cm-3 leads to a 50% increase of the differential gain for FP lasers at 25°C. Heavily doped devices also exhibit more rapid reduction of the differential gain with increasing temperature. The effect of active region doping on the energy separation between the electron Fermi level and electronic states coupled into the laser mode explains the observations. The temperature dependence of differential gain for DFB devices strongly depends on the detuning of the lasing wavelength from the gain peak [ABSTRACT FROM PUBLISHER]