L. M. Fedorov

The dislocation origin and model of excess tunnel current in GaP p-n structures

An excess tunnel current in GaP epitaxial nondegenerate p-n junctions on GaP and Si substrates was studied. An important experimental result is that the slope of exponential current-voltage (I–V) characteristic (in lnI–V coordinates) is independent of the width of the space-charge region, i.e., on n-and p-region doping levels. This fact is unexplained by existing models. A dislocation shunt model based on multihop tunneling through a dislocation line, which may be considered as a chain of parabolic potential barriers, is proposed. The density of dislocations predicted by this model is in agreement with the transmission electron microscopy (TEM) observations.

Determination of the Free Carrier Concentration in Ultra-Pure GaAs Epilayers by a Photoreflectance Technique

A new method for the diagnostics of high-quality n-GaAs epilayers grown by vapor phase epitaxy in an open chloride system has been developed and implemented. As the free carrier concentration in the material decreases from 1015 to 1011 cm−3 and the quality of epilayers increases, the photoreflectance spectra of GaAs exhibit a change from the traditional Franz-Keldysh (FK) oscillations (enhanced by the exciton effects) to a weak oscillatory structure observed in the region of exciton transition energies. It is shown that the periods of this structure are close to that of the FK oscillations.

GaAs p - i - n structures for X-ray detectors grown on Ge and GaAs substrates

Features of the creation of gallium arsenide (GaAs) p-i-n structures on germanium substrates are considered. Optimum regimes for growth of thick GaAs layers by hydride-chloride vapor phase epitaxy (HVPE) on Ge substrates are established, which allow high-quality p-i-n structures with characteristics close to those reached by homoepitaxy to be obtained. The spectra of exciton photoluminescence have been measured for ultrahigh-purity GaAs layers of various thicknesses grown under differing HVPE conditions.

GaAs P-I-N structures as detectors of x-ray radiation

Novel epitaxial growth regimes have been identified to grow thick layers of pure GaAs (up to 250 mcm) of large area in a single growth experiments by gas phase epitaxy. Characteristics of semiconductor epitaxial p-i-n structures based on GaAs have been studied. The obtained layers of i-GaAs have residual impurity concentration < 1012 cm−3. Pilot samples of x-ray radiation detector have been fabricated and energy resolution of the devices was about 600 eV at the absorbed photons energy of 60 keV and 200 eV at 5.9 keV, respectively.

Generating broadband random Gaussian signals

General approaches to the problem of generating random Gaussian signals are considered, a variant of practical implementation of such a generator is proposed, some technological aspects of the formation of active device structures are discussed, and spectral characteristics of the output noise signal are presented. The technical solution is based upon the principle of additive formation of a Gaussian process as a result of the joint operation of a group of parallel connected pulsed signal sources of the microplasma type. The proposed devices were implemented as GaAs microchips with p-n structures fabricated by epitaxial-diffusion technology, on which a matrix relief of elementary noise sources was formed using the microlithography techniques.

High-temperature gallium phosphide dynistors

Elements of the technology of gallium phosphide (GaP) epitaxial multilayer heterostructures grown by chemical vapor deposition in a chloride system are described and the main characteristics of GaP dynistors obtained by this method and intended for operation in a high-temperature (up to 400°C) medium are presented. A characteristic feature of the obtained initial epitaxial n-p-n-p structure is the binary zinc-magnesium doping of the p-emitter layer, which improves the device switching parameters (in particular, reduces the residual voltage at an acceptable level of reverse current) in comparison to those of the traditional Mg-doped structures. The observed optimization of the current-voltage characteristic is related to differences in the mechanisms of Zn and Mg diffusion in the GaP lattice, which can lead under certain conditions to suppression of the effect of structural defects present in the epilayers.

Photoelectric properties of GaN/GaP heterostructures

Thin interference layers of n-GaN were grown on n-and p-type GaP substrates with (100) and (111) orientations by vapor phase epitaxy in an open chloride system. Photosensitivity spectra of isotypic and anisotypic heterojunctions under linear polarized light from the side of the wideband component (GaN) at oblique incidence were investigated. Induced polarized photosensitivity was observed, and peculiarities of this photosensitivity caused by interference in the GaN layers are discussed.

Binary Acceptor Doping of Epitaxial Gallium Phosphide for High-Temperature Electronic Devices

We have experimentally studied the reverse-bias branch of the current-voltage (I–U) characteristics of high-temperature two-electrode devices (rectifying diode, Zener diode, hot electron emitter), the technology of which involves the stage of binary zinc-magnesium doping. Factors leading to the development of various types of the avalanche breakdown are analyzed as dependent on the Zn/Mg ratio. Differences in the characteristics and behavior of the I–U curves are related to features of the acceptor diffusion, which always accompanies the process of doping involved in the growth of multilayer epitaxial p–n structures.

Behavior of epitaxial GaAs layers as α particle detectors

The properties of epitaxial GaAs-based p+-n structures used as light-ion (α particle) were studied. A comparison is made with the latest published data on the possibilities of present-day semi-insulating GaAs (SI-GaAs). It is noted that the content of impurities and structural defects forming deep levels in the band gap of the material is two orders of magnitude lower in epitaxial layers. The deep levels determine the conditions of transport of nonequilibrium carriers in the detector, allowing for trapping of the carriers, and they also determine the electric-field profile. The charge-carrier lifetime was found to be ≥ 200 ns. This is two orders of magnitude longer than the values for SI-GaAs, in complete agreement with the lower content of deep centers. It is shown how deep centers influence the field profile, forming a quite large region of low field values.

Prolonged decay of free-to-bound photoluminescence in direct band gap InGaAs and AlGaAs alloys: Magnetic resonance studies

We report the observation of long nonexponential decays of free-to-bound photoluminescence (PL) in direct-gap AlGaAs and InGaAs alloys. The millisecond-long decay of band-to-acceptor PL at low temperatures found previously in GaAs, which contradicts the accepted recombination model, is demonstrated in AlxGa1−xAs with x up to 3% and InxGa1−xAs with the largest x used of 0.3%. The mechanism of the long PL decays, which were tentatively attributed to repeated trapping of free electrons by shallow donors, was studied using a magnetic resonance technique to selectively excite the 1s0–2p+1 transitions in donors. We find that the long PL decays resonantly respond to the selective donor excitation by far-infrared laser radiation in a magnetic field, thus supporting the donor-controlled trapping model. An improvement in the PL technique resolving power due to the use of the donor excitation is demonstrated. We show that the band-to-acceptor and donor-to-acceptor bands in ternary compounds, usually smeared due to the alloy disorder and/or built-in electric field effects, can be observed separately in time-delayed PL spectra taken under the conditions of the resonant excitation of shallow donors. Moreover, weaker bands hidden beneath the dominating ones can be revealed due to the use of donor excitation.