A. V. Murel

Usage of antimony segregation for selective doping of Si in molecular beam epitaxy

An original approach to selective doping of Si by antimony (Sb) in molecular beam epitaxy (MBE) is proposed and verified experimentally. This approach is based on controllable utilization of the effect of Sb segregation. In particular, the sharp dependence of Sb segregation on growth temperature in the range of 300–550 °C is exploited. The growth temperature variations between the kinetically limited and maximum segregation regimes are suggested to be utilized in order to obtain selectively doped structures with abrupt doping profiles. It is demonstrated that the proposed technique allows formation of selectively doped Si:Sb layers, including delta (δ-)doped layers in which Sb concentrations can be varied from 5 × 1015 to 1020 cm−3. The obtained doped structures are shown to have a high crystalline quality and the short-term growth interruptions, which are needed to change the substrate temperature, do not lead to any significant accumulation of background impurities in grown samples. Realization of the p...

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.

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.

Determination of the density of states in quantum wells and quantum dot arrays by the capacitance-voltage method

The possibility of determining the electronic density of states in quantum wells and quantum dot arrays in heterostructures from the capacitance-voltage curve is investigated. In heterostructures fluctuations of the composition and geometrical dimensions play an important role. It is shown that to reconstruct the exact density of states from the measured capacitance-voltage curve is impossible, because this problem is ill-posed from the mathematical point of view. An approximate method is proposed for solving the problem, involving the determination of a “reduced” density of states. It is shown that the reduced density of states is close to the true density if the characteristic energy scale governing the variation of the latter is much greater than the thermal energy kT. The proposed method is used to find the density of states in the conduction band of a quantum well in an In0.22Ga0.78As/GaAs heterostructure.

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.

Diagnostics of low-barrier Schottky diodes with near-surface δ-doping

To find the parameters of low-barrier Schottky diodes, a diagnostics technique based on an analysis of the dependence of the differential resistance of a diode with a Mott barrier and near-surface δ-shaped doping is developed. It is shown that a complete description of the current-voltage characteristics of the diode is possible with regard to the series n−-n+ junction. The technique makes it possible to optimize diodes to attain higher detection sensitivity.

Properties of Mott contacts with an ultralow metal-semiconductor barrier

The current-voltage and capacitance characteristics of Mott contacts with an ultralow metal-semiconductor barrier are investigated. The analysis is based on the analytical solution of the Poisson equation for the space charge of carriers in the “metal-i-layer-n+-substrate” structure without regard for bulk doping of the i layer. For contacts with ultralow metal-semiconductor barriers (comparable in magnitude to the thermal energy of charge carries), it is demonstrated that the reverse current becomes greater than the forward current, the sign of rectification is reversed, and the capacitance of the contact acquires a strong dependence on the voltage. This means that the mechanism of nonlinearity of the structure changes and the nonlinearity governed by charge carriers injected into the i layer becomes dominant. In a specific range of bias voltages close to zero, the differential resistance and the capacitance of the structure exponentially increase with increasing voltage. The observed behavior is not typical of conventional metal-semiconductor contacts. The obtained dependences of the electric current and capacitance on the voltage determine the characteristics of new advanced instruments, in particular, highly sensitive microwave detectors operating without a bias voltage.

Method of selective doping of silicon by segregating impurities

An original method for the controlled doping of silicon by segregating donor impurities is proposed. The approach is based on a rapid variation of the growth temperature during the molecular beam epitaxy between the regimes of kinetically limited segregation and maximum segregation of the dopant. By example of antimony, it is demonstrated that the proposed method can be used to obtain several-nanometer-thick selectively Sb-doped Si epilayers, in which a tenfold change in the volume concentration of the dopant is achieved on a 2–3 nm scale.

Photoluminescence up to 1.6 μm of quantum dots with an increased effective thickness of the InAs layer

Multilayered InAs/GaAs quantum dot (QD) heterostructures are produced by metal-organic gas phase epitaxy. The structures exhibit photoluminescence around 1.55 μm at 300 K. The specific feature of the technology is the growth of an InAs layer with an increased effective thickness deff to form QDs, in combination with low-temperature overgrowth of the QDs with a thin (6-nm) GaAs layer and with the annelaing of defects. By X-ray diffraction analysis and PL studies, it is shown that, in a structure with the increased thickness deff, a secondary wetting InGaAs layer is produced on top of the QD layer from the growing relaxed large-sized InAs clusters on annealing. A new mechanism of formation of large-sized QDs characterized by a large “aspect ratio” is suggested. The mechanism involves the 2D–3D transformation of the secondary InGaAs layer in the field of elastic strains in previously formed QDs. The specific feature of the array of QDs is the coexistence of three populations of different-sized QDs responsible for the multimode photoluminescence in the range from 1 to 1.6 μm. The potentialities of such structures for infrared photoelectric detectors operating in the range from 1–2.5 μm at room temperature are analyzed.