V. I. Shashkin

Control of charge transport mode in the Schottky barrier by δ-doping: Calculation and experiment for Al/GaAs

The possibility of controlling the effective barrier height in Schottky diodes by introducing a δ-doped layer near the metal-semiconductor contact is considered. A decrease in the effective barrier height is caused by the increased role of carrier tunneling through the barrier. A complete quantum-mechanical numerical simulation of the effect of the δ-layer parameters (concentration and depth) on the current-voltage characteristics of modified diodes was carried out for the Schottky barrier contacts to n-GaAs. The simulation results were found to fit well the experimental characteristics of diodes produced by metal-organic chemical vapor epitaxy. The studies carried out made it possible to choose the optimal δ-layer parameters to produce low-barrier (about 0.2 eV) diodes with a reasonable nonideality factor (n≤1.5). Such structures can be employed to fabricate microwave detector diodes without bias.

Theory of tunneling current in metal-semiconductor contacts with subsurface isotype δ-doping

The theory of tunneling current in metal-semiconductor contacts with subsurface isotype δ-doping is developed. Analytical expressions for current that take into account the decrease in the potential barrier height due to the image forces are obtained using the Murphy-Good approach. Characteristics of δ-doping that provide effective thermal field emission at the metal-semiconductor contact and a decrease in the effective barrier height from the original value to several kT are calculated. It is established that the main voltage dependence of the current in a contact with isotype δ-doping is exponential. It is shown that the nonideality factor can remain small (n≤1.07) for all values of the barrier height. A dramatic increase in n to the values n≥1.5 is typical of contacts with a partially depleted layer.

Segregation of indium in InGaAs/GaAs quantum wells grown by vapor-phase epitaxy

Distribution of indium atoms in structures which contained double InGaAs/GaAs quantum wells and were grown by vapor-phase epitaxy from metal-organic compounds was studied. Experimental indium-concentration profiles were obtained using Auger electron spectroscopy. A model of growth with allowance made for indium segregation and a model for the Auger profiling were used in the calculations of profiles. Fitting calculated profiles to experimental ones made it possible to estimate the activation energies for In-Ga exchange in the context of a kinetic model for segregation. These energies are found to be somewhat higher than those that are well known for molecular-beam epitaxy, which is related to stabilization of the growth surface by hydrogen atoms in a vapor-phase reactor.

Infrared lateral photoconductivity of InGaAs quantum dot heterostructures grown by MOCVD

Abstract InGaAs/GaAs quantum dots (QD) multilayer modulation-doped structures for infrared photodetector application were grown by the low-pressure metalorganic chemical vapor deposition. Normally incidence photoconductivity (PC) with a lateral electron transport was observed in samples, when the In supply during the QD formation was varied. At low temperature (near 4 K ) PC peak was observed near 16 μm . With increasing temperature another PC peak appeared near 5 μm .

InGaAsN/GaAs QD and QW structures grown by MOVPE

InGaAsN/GaAs heterostructures were grown by low pressure MOVPE. Their structural and optical properties were investigated. Pseudomorphic InGaAsN/GaAs layers with a band gap as low as 0.9 eV as well as ternary InAsN quantum dot and well structures were fabricated. It was shown that the addition of a few percent of nitrogen during the formation of the InAs quantum dots led to a decrease in their dimensions and density which was also accompanied by a sharpening of their uniformity distribution. An increase of the nitrogen content reduced the lattice mismatch between InAsN and GaAs. This also gave rise to a layer-by-layer growth mode and smooth heterointerfaces. The InAsN/GaAs multiple quantum well heterostructures so fabricated had improved structural quality and demonstrated intense photoluminescence at room temperature. r 2002 Published by Elsevier Science B.V.

Growth of BGaAs layers on GaAs substrates by metal-organic vapor-phase epitaxy

BxGa1−xAs layers were grown on GaAs substrates using low-pressure metal-organic vapor-phase epitaxy. Triethylboron, trimethylgallium, and arsine were used as boron, gallium, and arsenic sources. Optimum growth conditions were selected. The layers were studied using X-ray diffraction, secondary-ion mass spectrometry (SIMS), and photocurrent spectroscopy (PCS). The SIMS results showed a uniform boron distribution over the layer thickness. According to the PCS data, the BGaAs band gap decreases as the boron concentration increases.

Electrical properties of metal-semiconductor nanocontacts

Potential distributions around spherical and cylindrical metallic nanocontacts in semiconductors are calculated. Electrical properties of nanocontacts of small characteristic size ≪ (S is the width of the depletion region in planar geometry) are analyzed. It is shown that, compared to the planar case, nanocontacts have a weaker voltage dependence of the capacitance, a greater decrease in the Schottky barrier height due to the image forces, and a faster response up to frequencies in the terahertz range.

Single-crystalline GaAs, AlGaAs, and InGaAs layers grown by metalorganic VPE on porous GaAs substrates

Conditions for the growth of single-crystalline GaAs, AlGaAs, and InGaAs layers by metalorganic VPE were established and the corresponding semiconductor films were obtained on porous GaAs substrates. Comparative data on the morphology, structure, and electrical homogeneity of the epitaxial layers grown on the porous and monolithic substrates are presented. It was found that passage to the porous substrates leads to changes in the film growth rate and morphology, the concentration of electrically active defects, and their distribution in depth of the epitaxial structures.

Features of GaN Growth Attained by Metal-Organic Vapor-Phase Epitaxy in a Low-Pressure Reactor

The properties of GaN layers grown by metal-organic vapor-phase epitaxy on sapphire substrates at atmospheric and reduced pressures were studied. The surface morphology, crystalline, luminescence, and electric transport properties of these structures were comparatively analyzed. The depth profiles of elements were measured using secondary-ion mass spectrometry. The carrier distribution in heavily doped structures with p-n junctions was analyzed by electrochemical C–V profiling. It was shown that GaN layers grown in a low-pressure reactor feature improved structural, electric, and optical characteristics.

Deep states in silicon δ-doped GaAs

The density and electron trapping cross section of deep states in silicon δ-doped GaAs were investigated by means of measurements of the voltage and temperature dependences of the impedance of a Schottky contact to the structure. It was observed that density-of-states tails appear in the band gap when the silicon density in the d-layer exceeds 6×1012 cm−2. In our structures the energy characterizing the penetration depth of a tail was in the range 20–100 meV. The characteristic electron trapping cross section of deep states in δ-layers was of the order of 10−17 cm2. It was shown that saturation of the electron density in the δ-layer with increasing Si density is due to self-compensation of Si.