V. M. Danil’tsev

Optical monitoring of technological parameters in metal-organic vapor-phase epitaxy

The possibility of applying low-coherent tandem interferometry to optical monitoring of the temperature of a semiconductor substrate and the thickness of a deposited layer in metal-organic vapor-phase epitaxy (MOVPE) is demonstrated for the first time. The absolute accuracy in the temperature measurements of Si, GaAs, and sapphire substrates under MOVPE conditions is limited by the calibration accuracy and is ±1°C. The accuracy in the measurement of the deposited layer thickness is 2 nm. A considerable (10–100°C) deviation of the temperature measured by a thermocouple placed inside a susceptor from the actual substrate temperature is found. A significant temperature gradient along the susceptor depending on the gas flow rate and other factors is revealed. It is shown that, owing to the high heating efficiency of sapphire substrates, there is no need to coat their reverse with absorbing layers upon heating up to 300°C or in the presence of hydrogen pressure of higher than 100 mbar.

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.

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.

Quantitative analysis of the elemental composition and electron concentration in AlGaN/GaN heterostructures with a two-dimensional electron channel by means of SIMS and C-V profiling

The elementary composition and electron concentration in series of delta doped heterostructures AlXGa1 − XN/GaN with a two-dimensional electron channel are investigated. Separation of the electron channel and the doping Si admixture is shown by a combination of SIMS and C-V profiling.

Room-temperature photoconductivity in the 1–2.6 µm range in InAs/GaAs heterostructures with quantum dots

We have studied the room-temperature photoconductivity in the wavelength range 1–2.6 μm in InAs/GaAs heterostructures with quantum dots (QDs). Specific features of these heterostructures grown using the metalorganic vapor phase epitaxy (MOVPE) were an increase in the amount of InAs during the formation of a sheet of QDs and the use of alternating low-and-high-temperature regimes during their overgrowth with a GaAs barrier layer. For the first time, the MOVPE-grown multilayer InAs/GaAs heterostructures with quantum dots exhibited photoluminescence in a wavelength range of up to 1.6 μm and the photoconductivity up to 2.6 μm at room temperature. The heterostructures exhibited a room-temperature voltage sensitivity of 3 × 103 V/W (within a Si-plate filter bandwidth) and a specific detectivity of 9 × 108 cm Hz1/2 W−1.

The sandwich InGaAs/GaAs quantum dot structure for IR photoelectric detectors

A new possibility for growing InAs/GaAs quantum dot heterostructures for infrared photoelectric detectors by metal-organic vapor-phase epitaxy is discussed. The specific features of the technological process are the prolonged time of growth of quantum dots and the alternation of the low-and high-temperature modes of overgrowing the quantum dots with GaAs barrier layers. During overgrowth, large-sized quantum dots are partially dissolved, and the secondary InGaAs quantum well is formed of the material of the dissolved large islands. In this case, a sandwich structure is formed. In this structure, quantum dots are arranged between two thin layers with an increased content of indium, namely, between the wetting InAs layer and the secondary InGaAs layer. The height of the quantum dots depends on the thickness of the GaAs layer grown at a comparatively low temperature. The structures exhibit intraband photoconductivity at a wavelength around 4.5 μm at temperatures up to 200 K. At 90 K, the photosensitivity is 0.5 A/W, and the detectivity is 3 × 109 cm Hz1/2W−1.

Effect of B atoms on the properties of InAs quantum dots in the GaAs matrix

The effect of B dopants on the properties of InAs quantum dots is studied experimentally. It is shown that the incorporation of B atoms decreases the integral amount of InAs that is needed to form islands according to the Stransky-Krastanov mechanism and leads to an increase in the density of dots. At the same time, it is discovered that the sensitivity of InAs quantum dots to annealing increases, which leads to the degradation of the optical properties of these quantum dots during growth of covering layers.

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.

Subnanometer Resolution in Depth Profiling Using Glancing Auger Electrons

A new method for Auger depth profiling, employing a difference in the escape depth of the Auger electrons emitted at nearly normal and glancing angles, is proposed and verified. The depth profiles obtained under optimum ion sputtering conditions with registration of the glancing Auger electrons exhibit a subnanometer (0.8 nm) depth resolution. This technique was successfully applied to the study of high-quality InxGa1−xAs/GaAs heterostructures with quantum wells grown by the method of metalorganic chemical vapor deposition.

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.