Yu. G. Sidorov

Molecular beam epitaxy of high quality Hg1 − xCdxTe films with control of the composition distribution

Abstract An investigation of Hg 1 − x Cd x The heterostructure (MCT HS) growth processes using in situ ellipsometry by molecular beam epitaxy (MBE) was carried out. High quality MCT HS with a low density of V-shaped defects (near 10 2 cm −2 ) were grown on (103) GaAs substrates. Electron probe micro analysis (EPMA) revealed the presence of elemental tellurium inside the V-shaped defects. The appearance of V-shaped defects was connected with processes in which tellurium molecules take part on the growing surface. The MCT HS with wide band gap layers at the interface with the substrate and at the surface had the best electrical characteristics. In as-grown n-type material the electron concentrations, mobilities and life time of the minority carriers were 2 × 10 14 –5 × 10 15 cm −3 , 50000–350000 cm 2 /V · s, and up to 10 −6 s, respectively. In as-grown p-type material the hole concentrations, mobilities and life time of the minority carriers were 5 × 10 15 –2 × 10 16 cm −3 , over 500 cm 2 /V · s, and over 10 −7 s, respectively. Photoconductors and photodiodes were fabricated on the base of MCT HS with good photoelectrical parameters.

Molecular-beam epitaxy of mercury-cadmium-telluride solid solutions on alternative substrates

Growth processes were considered for heteroepitaxial structures based on a mercury-cadmium-telluride (MCT) solid solution deposited on GaAs and Si alternative substrates by molecular-beam epitaxy. Physical and chemical processes of growth and defect-generation mechanisms were studied for CdZnTe epitaxy on atomically clean singular and vicinal surfaces of gallium-arsenide substrates and CdHgTe films on CdZnTe/GaAs surfaces. ZnTe single-crystalline films were grown on silicon substrates. Methods for reducing the content of defects in CdZnTe/GaAs and CdHgTe films were developed. Equipment for molecular-beam epitaxy was designed for growing the heteroepitaxial structures on large-diameter substrates with a highly uniform composition over the area and their control in situ. Heteroepitaxial MCT layers with excellent electrical parameters were grown on GaAs by molecular-beam epitaxy.

Peculiarities of the MBE growth physics and technology of narrow-gap II–VI compounds

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. Experimental research and a crystallochemical consideration of the chemical interaction of the film and substrate components in the A 2 B 6 /GaAs heterostructure were carried out. It was found that surface faceting, twinning and breaking of stoichiometry of the growing structure can be explained by the excess of valent electrons at the A 2 B 6 /GaAs interface. The films were grown in a multichamber mercury cadmium telluride (MCT) MBE system with different compositions of the residual gas phase in different chambers. The MCT growth chamber is equipped with a system of molecular sources of original design and a built-in automatic ellipsometer. The used system of sources allows for growing MCT films without sample rotation, uniform in composition over the substrate area of 51 mm in diameter (the composition gradient does not exceed 0.002 cm −1 ). Because there is no substrate rotation, continuous measurements of film composition can be performed during growth, and structures with specified composition over thickness can be grown. The introduction of layers with a varying energy gap into the heteroepitaxial structure increases the carriers lifetime up to 2 μs for x=0.22 (77 K). A model of defects, determining the electric parameters of MBE grown films in the presence of gallium sources, is suggested. Linear photoconductor arrays for the 8-12 μm band with background limited parameters were fabricated from the grown MCT films.

Defect formation during growth of CdTe(111) and HgCdTe films by molecular beam epitaxy

(111)B CdTe films and (111)B and (112)B HgCdTe films were grown by MBE. The films were examined by optical and transmission electron microscopy. Formation of the microtwins and dislocations was observed in the films. The HgCdTe films contained some complicated defects also. The interaction of partial dislocations in the twinning plane results in the creation of threading dislocations. The increase of twin boundary density leads to an increase of the threading dislocation density in CdTe (111)B films. The existence of the elemental tellurium phase is possible during Hg0.8Cd0.2Te film growth by MBE. This circumstance in combination with the twinning process leads to the avalanche-type multiplication of the structure defects.

The controlled growth of high-quality mercury cadmium telluride

The investigations of HgCdTe heterostructures (MCT HS) and molecular beam epitaxy (MBE) growth processes using in-situ ellipsometry were carried out. The high-quality MCT HS with low density of V-shape defects (10 2 cm -2 ) were grown on (103) CdTe and GaAs substrates. The MCT HS with wide band gap layers at the interface and at the surface exhibited the best electrical characteristics. The electron concentrations, mobilities and life-time of minority carriers were 2 X 10 14 -5 X 10 15 cm -3 , 50000-350000 cm 2 V -1 s -1 , 10 -6 s, respectively. The hole concentrations, mobilities and life-time of minority carriers were 5 X 10 15 -2 X 10 16 cm -3 , above 500 cm 2 V -1 s -1 , 10 -7 s, respectively. On the base of the grown MCT HS, photoconductors and photodiodes were fabricated with good photoelectrical parameters. Electron probe microanalysis studies revealed the presence of elemental tellurium inside V-shape defects. Thermodynamic calculations suggested the possibility of elemental tellurium crystallization during the MCT HS growth by MBE.

Photoluminescence of Hg1 − xCdxTe based heterostructures grown by molecular-beam epitaxy

Photoluminescence (PL) of Hg1 − xCdxTe-based heterostructures grown by molecular-beam epitaxy (MBE) on GaAs and Si substrates has been studied. It is shown that a pronounced disruption of the long-range order in the crystal lattice is characteristic of structures of this kind. It is demonstrated that the observed disordering is mostly due to the nonequilibrium nature of MBE and can be partly eliminated by postgrowth thermal annealing. Low-temperature spectra of epitaxial layers and structures with wide potential wells are dominated by the recombination peak of an exciton localized in density-of-states tails; the energy of this peak is substantially lower than the energy gap. In quantum-well (QW) structures at low temperatures, the main PL peak is due to carrier recombination between QW levels and the energy of the emitted photon is strictly determined by the effective (with the QW levels taken into account) energy gap.

Defect structure of HgCdTe films grown by molecular beam epitaxy on Si substrates

An ion milling-assisted study of defect structure of HgCdTe films grown by molecular beam epitaxy on Si substrates was performed. The films appeared to contain initially neutral Te-related defects with concentration of 1017 cm−3, typical of HgCdTe. The concentration of residual donors was found to be quite low ((3–8) × 1014 cm−3). Specific to HgCdTe/Si technology appeared to be a considerable number of stacking faults, which affected the carrier mobility in n-type material. These defects can be annealed in He atmosphere at 230 °C, and after ion milling the electrical parameters of n-type HgCdTe/Si films approach those of high-quality bulk crystals.

Donor doping of HgCdTe for LWIR and MWIR structures fabricated with ion milling

Ion milling was used to establish the minimum donor doping level Nmd required for obtaining n-regions with reproducible electron concentration in HgCdTe-based LWIR and MWIR device structures fabricated with ion treatment. The experiments were performed on n-type films grown by molecular beam epitaxy, un-doped and in situ doped with indium with the concentration NIn = 5 × 1014–1017 cm−3. A study of the electrical properties of the milled films showed that Nmd comprised ~2 × 1015 cm−3 for the LWIR and ~5 × 1015 cm−3 for the MWIR films. In the films with NIn exceeding these critical values, the electron concentration after the milling strictly followed the doping. A need for consideration of the disintegration of the milling-induced defects is also shown.

Ellipsometry as a powerful tool for the control of epitaxial semiconductor structures in-situ and ex-situ

Abstract The results of the consistent use of in-situ and ex-situ ellipsometry as a control of MCT/CdTe/GaAs heterostructures growth by molecular beam epitaxy (MBE) are presented. It is shown that ellipsometry is able to control the quality of a GaAs substrate preparation prior to epitaxy, to measure the buffer layers and MCT films growth rate, to monitor in-situ composition and surface morphology during deposition process. Temperature measurements of CdTe dielectric functions were made which show the possibility of in-situ determination of surface temperature.

Nucleation of epitaxial films at chemical growth

Abstract A theoretical analysis and an experimental investigation of nucleating epitaxial Ge and GaAs films under chemical transport conditions at homoepitaxy were made. Estimation of nucleation rate was made taking into account the differences of temperature between the source and deposition zones, substrate orientation and its surface state. Investigation of crystallite nucleation and growth was carried out by electron-microscope replica method for deposition time from 5 sec up to 1 hour. The nucleus distribution curves of size and changes of nucleus density and size with time were obtained. The initial stage of deposition of GaAs occurs by forming three-dimensional nuclei and their growth occurs at constant rate. Nucleation rate defines the film perfection and its minimal thickness. The change of the nucleus form with time is observed and the role of the diffusion process is discussed.