R. Magnanini

Electrical and photoluminescence properties of undoped GaSb prepared by molecular beam epitaxy and atomic layer molecular beam epitaxy

Abstract High-quality, unintentionally doped GaSb layers were grown by molecular beam epitaxy (MBE) and by atomic layer MBE (ALMBE) to study the influence of growth conditions on their transport and photoluminescence properties. While the hole mobility μ is only slightly dependent on the growth conditions, the 77 K hole concentration p shows minima at growth temperatures of ∼ 450°C and for Sb 4 /Ga beam equivalent pressure ratios (BEPRs) of ∼ 8; the concentrations of singly and of doubly ionizable acceptors and of a compensating donor have been obtained by simultaneously fitting the temperature dependence of μ and p in the 40–300 K range; from these results we show that the existence of minima of p can be related to an increased electrical compensation due to a reduced incorporation of acceptors. The 15 K photoluminescence spectra are generally dominated by the donor-acceptor pair transition (A, 779 meV) involving the neutral state of the native acceptor, except when the growth is carried out at relatively low temperatures with low BEPRs. Under the latter conditions: (i) a peak (788 meV) shows at an energy 25 meV below the band-gap energy and (ii) exciton related transitions have intensities comparable to that of the A recombination.

Composition control of GaSbAs alloys

AbstractWe report on a detailed study on the dependence of GaSb!As#!alloy composition (x(0.5) on the #uxes of theindividual constituents Ga, Sb and As. The values of #uxes are obtained by the analysis of RHEED oscillations underGa-, As- and Sb-limited growth conditions, while the alloy composition has been derived by the combined use ofphotoluminescenceand Rutherford backscatteringspectrometry measurements.It is shown that the Sb mole fraction: (i)increases with increasing Ga #ux when the other parameters are kept constant, (ii) increases with increasing Sb #ux and,(iii)forgivenGaandSb#uxes,is basicallyindependentofthe As#uxforrelativelyhighAs#uxes,whileitincreasesastheAs #uxes are reduced. The present results allow an improved control of composition of the GaSbAs alloys that areconsidered of increasing interest for optoelectronic applications. ! 1999 Published by Elsevier Science B.V. All rightsreserved. PACS: 81.15.Hi; 42.70.Km Keywords: MBE; III}V}V! alloys; GaSbAs 1. IntroductionGaSbAs is considered as a promising materialfor long-wavelength optoelectronic devices andultra-low-noise, very-high-frequency HEMTs [1].However, III}V}V! alloys have the drawback thatthe control of their composition is much moredi

Controlled intrinsic carbon doping in MOVPE-grown GaAs layers by using TMGa and TBAs

cult than that of the III}III!}V counterparts,duetothestrongcompetitionbetweenthe incorpo-rations of anions, which leads to di!erent stickingcoe

Determination of lattice parameters in the epitaxial AlSb/GaSb system by high resolution X-ray diffraction

cients of V and V! species. Moreover, growthrate measurements of the constituent binary mate-rials obtained by RHEED oscillations cannot beused to determine the alloy mole fraction which,instead, has to be obtained by additional tech-niques such as photoluminescence (PL), X-ray dif-fractionorRutherfordbackscatteringspectrometry(RBS).In this work, we have systematically studied thedependence of the GaSb!As#!composition(x(0.5) on the parameters that completely denethe composition of the nourishing phase, that are

Optical functions of bulk and epitaxial GaSb from 0.0025 to 6 eV

Abstract Homoepitaxial GaAs layers were grown by low-pressure metalorganic vapor phase epitaxy (MOVPE), by using the metalorganic precursors trimethylgallium (TMGa) and the low-toxicity, low-dissociation-temperature tertiary-butyl-arsine (TBAs), in order to exploit the phenomenon of controlled intrinsic carbon doping. Low-temperature photoluminescence, Hall effect and capacitance-voltage measurements were performed on the grown samples. The intrinsic carbon doping was studied as a function of: (i) the growth temperature (ranging between 500°C and 640°C), (ii) the V/III precursor ratio in the vapour phase (ranging between 1 and 25) and (iii) the influence of GaAs substrate mis-orientation (0° and 2°off toward 110). Although a reduced carbon incorporation rate was expected by using TBAs, which is a benefit in obtaining high purity GaAs, intrinsically p-doped GaAs layers with a hole concentrations up to 6.5×1018xa0cm−3 and a corresponding RT mobility in the range (100–400)xa0cm2/Vxa0s were obtained.

Electron mobility and physical magnetoresistance in n-type GaSb layers grown by molecular beam epitaxy

Abstract (001)-oriented AlSb GaSb heterostructures grown by molecular beam epitaxy under optimized conditions have been studied by high resolution X-ray diffraction (HRXRD) in order to measure the lattice parameter aAlSb and the Poisson ratio v[001]AlSb of epitaxial AlSb with high accuracy. The knowledge of these parameters is a prerequisite for the measurement of the composition of Al1 − xGaxSb ternary solutions by means of X-ray diffractometry. The thicknesses of AlSb layers have been chosen so as to result in pseudomorphic and almost completely relaxed layers. The HRXRD investigations have been carried out using the 004, 335 and 117 reflecting planes, as well as the near vertical 551 reflecting planes, with a symmetrical beam path, which give high sensitivity to the parallel component of mismatch. The data on epitaxial AlSb (aAlSb = 6.1353 ± 0.0003A and v[001]AlSb = 0.328 ± 0.005) are in excellent agreement with the previously published data, but have better accuracy and reliability.

Preparation of GaSb by molecular beam epitaxy and electrical and photoluminescence characterization

Abstract The complex refraction index and dielectric functions of GaSb bulk (both p and n -type) and MBE film were accurately determined from 0.0025 to 6 eV by using reflectance and ellipsometric spectroscopies. These functions, which satisfy the Kramers-Kronig causality relations, appear independent on the doping (≤2×10 17 cm −3 ) in the interband transition region. In particular, in comparison with previous data from literature, the E 0 fundamental gap is well evidenced for all the samples. Moreover, the optical functions around the gap are very different from those previously reported and the refractive index was modeled by a Sellmeier dispersion relation. The free-carriers instead strongly influence the far-infrared restrahlen region due to the phonon-plasmon coupling. In this range the optical functions were well fitted by Drude-Lorentz oscillators.

Measurement of aluminum concentration in the Ga1−xAlxSb/GaSb epitaxial system

Electron mobility and low-field transverse physical magnetoresistance were measured in Te-doped GaSb layers grown by molecular beam epitaxy. The samples investigated had electron densities ranging from to ; measurements were taken in the 8 - 300 K temperature range. The high mobility values demonstrate that SnTe can be used as a source of Te doping with results comparable with GaTe. A detailed analysis of the magnetoresistance data demonstrates that in samples with high electron density the magnetoresistance is mainly due to mixed conduction of electrons in both and L conduction band minima: the analysis gives the temperature dependence of the and mobilities and of the energy separation between L and edges. is 82 meV at 300 K and 67 meV at 8 K and exhibits a non-monotonic behaviour within the temperature range explored. In samples with low electron density the magnetoresistance is mainly due to the energy distribution of carriers in the valley.

Interband optical properties of molecular-beam epitaxially grown GaAs1−xSbx on GaAs substrates

Abstract The molecular beam epitaxy and the characterization of high-quality, non-intentionally doped and Te-doped GaSb are reported. The undoped layers have 77 K Hall hole concentrations p = 1−3 × 10 15 cm −3 and mobilities μ = 3000−5600 cm 2 V −1 s −1 , which compare favourably with the best results reported so far. Photoluminescence (PL) measurements at 70 K point to a relatively low concentration of intrinsic GaSb antisite defects, responsible for the p-type behaviour. A simultaneous fit of μ and p was performed in the 40–300 K temperature range by using a model with two acceptors, one of them having two charge states; the levels have energies consistent with those deduced by PL experiments. n-Doping was obtained approximately in the range 1 × 10 16 −1 × 10 18 cm −3 by using Te from an SnTe source. The mobility values are definitely higher than those reported in the literature and obtained with the same source, and they slightly exceed those achieved in GaSb doped using a GaTe Te source. A procedure for the analysis of electrical data has been set up and tested for n-GaSb with free carrier concentrations lower than a few 1017 cm−3.

Lattice strain relaxation study in the Ga1−xAlxSb/GaSb system by high resolution x-ray diffraction

The composition of several Ga1−xAlxSb epitaxial layers of different thicknesses grown by molecular beam epitaxy on GaSb with x ranging between 0.1 and 0.8, has been obtained independently by high resolution x-ray diffraction, Rutherford backscattering spectrometry, and reflection high-energy electron diffraction. From the comparison between the results obtained by the different experimental methods, it has been possible to point out that the lattice constant of the layer increases nonlinearly with the Al content. A comparison with theoretical models has been done. A phenomenological equation has been derived for a correct analysis of the x-ray results.