Strain effects in CdTe (111) epitaxial layers grown on GaAs (100) substrates by molecular beam epitaxy

Spectroscopic ellipsometry and photoreflectance measurements on CdTe/GaAs strained heterostructures grown by moleculclr beam epitaxy were carried out to investigate the effect of the strain and the dependence of the lattice parameter on the CdTe epitaxial layer thicknesses. Compressive strains exist in CdTe layers thinner than 2 μm. As the strain increases, the value of the critical-point energy shift increases linearly. These results indicate that the strains in the CdTe layers grown on GaAs substrates are strongly dependent on the CdTe layer thickness. Author to whom all correspondence should be addressed.     

Quantum transport of p-type GaAs/(AlGa)As heterostructures grown on non-(100) substrates by molecular beam epitaxy

We report on a series of Be-doped GaAs/(AlGa)As two-dimensional hole gas (2DHG) structures grown on (110), (111)B, (211)B and (311)B oriented substrates and compare their properties with high mobility samples grown on (311)A using Si doping. The samples were prepared and grown under the same conditions in order to render them comparable. They are found to have mobilities which are strongly anisotropic within the plane. All the samples show strong low-field positive magnetoresistance with resistance increases of up to 30% at magnetic fields of only 0.1 T. The presence of this feature on all the different planes shows that it does not depend upon the details of the band structure. It is identified with the lifting of the degeneracy of the spin sub-bands by the asymmetrical potential giving rise to a classical two-band magnetoresistance.

The modulation-doped GaAs/(AlGa)As heterostructures grown on the (311)A GaAs surface using silicon as the acceptor produced 2DHGs with low-temperature hole mobility exceeding 1.2 × 10⁶ cm² V⁻¹ s⁻¹ with carrier concentrations as low as 0.8 × 10¹¹ cm⁻². This hole mobility is the highest ever observed at such low densities by any growth technique. These 2DHG samples show for the first time the persistent photoconductivity effect. This effect is normally absent in 2DHG systems. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above 4 K and interface scattering at lower temperatures.     

Spatially resolved Raman investigation of Si-doped GaAs layers on patterned GaAs(100) substrates grown by molecular beam epitaxy

Local carrier transport properties of Si-doped GaAs layers on ridge structures exhibiting (111)A and (111)B sidewalls are investigated. The layers were grown by molecular beam epitaxy at different substrate temperatures and As/Ga flux ratios. Using spatially resolved Raman spectroscopy we determine the type and density of free charge carriers (≥ 5 × 10¹⁷ cm⁻³) in the grown layers on the different index facets from an analysis of the coupled plasmon-longitudinal optical-phonon mode which was calibrated against Hall standards. We demonstrate that on the (100) and (111)B facets the regrown layers are n-type and on the (111)A facets p- or n-type depending on the growth conditions. Line scans of the carrier density show that the (100)/(111)A/(100) facet transition forms a graded lateral n-p-n junction. Spatially resolved photoluminescence measurements confirm our findings.     

Very high purity In0.53Ga0.47As grown by molecular beam epitaxy

Very high purity In0_0.53Ga_0.47As layers were grown by molecular beam epitaxy (MBE). Origins ofn-type impurities in undoped In_0.53Ga_0.47As grown on an InP:Fe substrate were systematically examined. The most possible origins were impurities diffusing from the InP:Fe substrate and those contained in As molecular beam. These impurities were dramatically reduced by using an InAlAs buffer layer and a growth condition of high substrate temperature and low As pressure. The lowest electron concentration of the In0_0.53Ga_0.47As layer wasn = 1.8 × 10¹³ cm_-3 with mobilitiesμ = 15200 cm²/Vs at 300 K andμ = 104000 cm²/Vs at 77 K.     

Photoluminescence and raman scattering characterization of silicon-doped In0.52Al0.48As grown on InP (100) substrates by molecular beam epitaxy

Growth of In_0.52Al_0.48As epilayers on InP (100) substrates by molecular beam epitaxy at different silicon doping levels is carried out. The doped samples show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. There is a reduction in both the AlAs-like and InAs-like longitudinal-optic (LO) phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased. The PL intensity also showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.     

Misfit relaxation behavior in CdHgTe layers grown by molecular beam epitaxy on CdZnTe substrates

Uniform layers of cadmium mercury telluride have been grown on inhomogeneous cadmium zinc telluride substrates by molecular beam epitaxy so that a single epitaxial layer experiences a laterally varying lattice mismatch. The lateral variations of layer and substrate lattice parameters, layer lattice tilt, diffraction peak width, etch pit density (EPD) and surface crosshatch have been characterized, and all measured quantities are reported as functions of the substrate lattice parameter. At small mismatch, the layer appears to be elastically deformed. Beyond a certain critical mismatch, the onset of relaxation is clearly observed in the layer lattice parameter. Relaxation leads to appearance of surface crosshatch and an increased diffraction peak width, but a reduction in EPD, suggesting a reduction in the density of threading dislocations within the layer.     

Highly strained ln0.35Ga0.65As/GaAs layers grown by molecular beam epitaxy for high hole mobility transistors

We have grown highly strained In_0.35Ga_0.65As layers on GaAs substrates by molecular beam epitaxy to improve the performance of high hole mobility transistors (HHMTs). The mobility and sheet hole concentration of double side doped pseudomorphic HHMT structures at room temperature reached 314 cm2/V-s and 1.19 × 10¹² cm⁻², respectively. Photoluminescence measurements at room temperature show good crystalline quality of the In^0.35Ga_0.65As layers. This study suggests that the performance of HHMTs can be improved by using high-quality In_0.35Ga_0.65As layers for the channel of double side doped heterostructures pseudomorphically grown on GaAs substrates.     

High uniformity of Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures grown by molecular beam epitaxy on 3″ GaAs substrates

Al_0.3Ga_0.7As/ln_0.15Ga_0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 μm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.     

Very high electron mobility In0.8Ga0.2As heterostructure grown by molecular beam epitaxy

A very high electron mobility pseudomorphic In_0.8Ga_0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of RHEED oscillations in an MBE system. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 and 16 m²/Vs at 293 and 10 K, respectively, is obtained.     

掺Te 的GaSb薄膜分子束外延生长及缺陷特性

分析了非掺GaSb材料及在GaAs衬底上用分子束外延生长掺杂Te的GaSb薄膜材料的缺陷特性,主要应用正电子湮没多谱勒展宽谱方法,并结合原子力显微镜和X射线衍射测试进行.多谱勒展宽谱研究表明,采用分子束外延法生长的掺杂Te的n型半导体GaSb薄膜材料的S参数比体材料小,所得缺陷主要是单空位与间隙原子,而几乎无复合体的缺陷类型.     

Super-flat interfaces in In0.53Ga0.47As/In0.52Al0.48As quantum wells grown on (411)A InP substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (“(411)A super-flat interfaces”) were successfully achieved in In_0.53Ga_0.47As/In_0.52Al_0.48As quantum wells (QWs) grown on (411)A InP substrates by molecular beam epitaxy (MBE) at a substrate temperature of 570°C and V/III=6. Surface morphology of the In_0.53Ga_0.47As/In_0.52Al_0.48As QWs was smooth and featureless, while a rough surface of those simultaneously grown on a (100) InP substrate was observed. Photoluminescence (PL) linewidths at 4.2 K from the (411)A QWs with well width of 0.6–12 nm were 20–30 % narrower than those grown on a (100) InP substrate and also they are almost as narrow as each of split PL peaks for those of growth-interrupted QWs on a (100) InP substrate. In the case of the (411)A QWs, only one PL peak with very narrow linewidth was observed from each QW over a large distance (7 mm) on a wafer.     

Effect of As overpressure on Si-doped (111)A, (211)A and (311)A GaAs grown by molecular beam epitaxy

Si-doped (111)A, (211)A and (311)A GaAs samples grown by molecular beam epitaxy (MBE) at different As over-pressures have been studied. Hall effect measurements have revealed that the doping changes from p- to n-type when the As pressure is increased. The transition As pressure is lower for the (211)A than for the (311)A surfaces. Photo-luminescence measurements have shown that, when the As pressure is increased, arsenic vacancy defects are changed into pairs of Ga vacancy and Ga antisite defects. These results are explained by considering the orientation dependence of the surface bonding and the kinetics of the MBE growth process.     

Antimony segregation in Si layers grown by molecular beam epitaxy on Si wafers with different crystallographic orientations

The segregation of Sb in Si layers grown by molecular beam epitaxy on Si substrates with the (111), (110), and (115) crystallographic orientations is studied; the results obtained for these orientations are compared with those obtained for the most widely used orientation (001). It is found that there is a qualitative similarity between the temperature dependences of the Sb segregation ratio (r) for all studied orientations; in particular, it is possible to separate two characteristic temperature ranges corresponding to the kinetically limited and equilibrium regimes of segregation. However, quantitatively, the values of r for the orientations under study differ significantly from those for the Si(001) case at the same temperatures. For all orientations, narrow temperature ranges within which the values of r vary by nearly five orders of magnitude are revealed for all dependences of r on the growth temperature. This finding allows us to adopt the method of selective doping, which was for the first time suggested by us for structures grown on Si (001) and is based on the controlled use of the segregation effect, to structures grown on Si substrates with an orientation different from (001). Using this method, selectively doped Si:Sb/Si(111) structures are fabricated; in these structures, a variation in the Sb concentration by an order of magnitude occurs at the scale of several nanometers.     

Influence of mismatch of the lattice parameters on the structural, optical, and transport properties of InGaAs layers grown by molecular beam epitaxy on InP(100) substrates

The influence of mismatch stress on the structural, optical, and transport properties of thick InGaAs layers grown on InP(100) substrates by molecular-beam epitaxy is investigated. It is found that layers having tensile stress can be grown with a greater mismatch than compressively stressed layers before plastic relaxation sets in. The critical mismatch for thick InGaAs layers is not described with sufficient accuracy by either the mechanical equilibrium model or the energy balance model. The range of mismatches required to obtain high carrier mobilities and high radiative recombination efficiencies in InGaAs layers grown on InP substrates is much narrower than the pseudomorphic growth range. The maximum mobilities and minimum widths of the photoluminescence peak are attained in layers matched with the substrate in terms of the lattice parameter and also in slightly gallium-enriched layers. The compositional dependence of the width of the band gap is investigated with allowance for the influence of stress. Fiz. Tekh. Poluprovodn. 31, 19–22 (January 1997)     

Antiphase boundary of GaAs films grown on Si(001) substrates by molecular beam epitaxy

Single and double domain GaAs film growth on double domain Si(001) substrates by molecular beam epitaxy were observed. The domain structure of the film did not succeed to the domain structure of the substrate surface but was decided by a direction of slight misorientation of the substrate. To explain this, it has been proposed that the antiphase boundary (APB) of the film is dominantly non-stoichiometric,i.e., the APB is composed of the same polar {11n} or {nn1} (n = 1, 2, ….) planes of the adjacent domains. Growth simulation based on this model about the APB has explained well the experimental results that a double domain film can grow on a Si(001) surface which is exactly oriented or is misoriented towards a 〈100〉 direction.     

pn-Junction photodiode based on GaN grown on Si (111) by plasma-assisted molecular beam epitaxy

The growth and characterization of pn-junction photodiode based on GaN grown on Si (111) by RF-plasma assisted molecular beam epitaxy (MBE) are described. The structural and optical properties of samples were studied by HR-XRD and Fourier FTIR spectroscopy, respectively. For IR reflectance analysis, GaN-like and AlN-like E₂ TO optical modes have been detected. By using the thermal evaporator, Ni/Ag and Al contacts were evaporated at the front and back of samples. The application of thermal annealing treatment in oxygen ambient has been shown to significantly reduce the dark current of GaN pn-junction photodiode. The electrical characteristics of all samples were conducted using Keithley's I–V measurement system. Under 460-nm wavelength, at bias voltages of 0.5, 1, and 2 V, the photocurrents rise and decay times were investigated.     

Polarization of in-plane photoluminescence from InAs/Ga(In)As quantum-well layers grown by metallorganic vapor-phase epitaxy

This paper investigates the linear polarization of photoluminescence emitted along the plane of an InAs/Ga(In)As wafer. The polarization was observed to depend on the asymmetry of the quantum-well shape, quantum-dot formation, and the presence of inclusions in the bulk alloy. Fiz. Tekh. Poluprovodn. 32, 1254–1259 (October 1998)     

Electrical transport properties of cerium doped Bi2Te3 thin films grown by molecular beam epitaxy

Introducing magnetism into topological insulators (Tls) can tune the topological surface states and produce exotic physical effects.Rare earth elements are considered as important dopant candidates,due to their large magnetic moments from heavily shielded 4f electrons.As the first element with just one 4f electron,cerium (Ce) offers an ideal platform for explor-ing the doping effect of f-electron in Tls.Here in this work,we have grown cerium-doped topological insulator Bi2Te3 thin films on an Al2O3(0001) substrate by molecular beam epitaxy (MBE).Electronic transport measurements revealed the Kondo effect,weak anti-localization (WAL) effect and suppression of surface conducting channels by Ce doping.Our research shows the funda-mental doping effects of Ce in Bi2Te3 thin films,and demonstrates that such a system could be a good platform for further re-search.     

Ultraviolet luminescence of thin GaN films grown by radical-beam gettering epitaxy on porous GaAs(111) substrates

GaN films with a thickness of 0.1 μm were grown by radical-beam gettering epitaxy on porous GaAs(111) substrates. Excitonic luminescence bands are dominant in the photoluminescence spectra measured at 4.2 K. The energy positions of excitonic-band peaks are analyzed; as a result, it is concluded that there are stresses in the grown GaN films. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 11, 2003, pp. 1303–1304. Original Russian Text Copyright ? 2003 by Kidalov, Sukach, Revenko, Potapenko.