Osamu Igarashi

HETEROEPITAXIAL GROWTH OF GaP ON SILICON BY MOLECULAR BEAM EPITAXY.

Heteroepitaxial GaP layers were grown on Si substrates, misoriented by 5° from the (111) face toward the [100] axis, by molecular beam epitaxy (MBE). The RHEED pattern of GaP is of elongated streaks, indicating that the quality of the grown layers is good. From observation by the X-ray divergent beam method, the [111] axis of the grown layers is parallel to that of the substrate. Autodoping of Si into the epitaxial layers from the substrate is very small compared with the layers grown by CVD. Photoluminescence was measured for GaP on Si which was irradiated with an ionized nitrogen beam during MBE.

Epitaxial Growth of CuGaS2 by Halogen Transport Method

CuGaS2 was epitaxially grown on (001) GaP and (110) GaAs by the halogen transport method. Orientation relationships in these cases were (a) [001]CuGaS2//[001]sub and [100]CuGaS2//[100]sub, and (b) [001]CuGaS2//[001]sub and [110]CuGaS2//[110]sub, respectively. Results of the growth on the other faces of the substrates (involving sapphire) were as follows. (1) On (001) GaAs, although the growth occurred with the relationship of (a) (or (c) [001]CuGaS2//[010]sub and [100]CuGaS2//[001]sub), twinning about [221] and [1] (or [21] and [22]) was observed. (2) The growth on (102) Al2O3 was essentially the same as (1). (3) On (110) GaP, the coexistence of two relationships, (c) and (d) [001]CuGaS2//[100]sub and [010]CuGaS2//[001]sub, was observed. (4) The CuGaS2 deposited on (0001) Al2O3 was composed of six sets of (112)-orientated crystallites which were rotated every 60° about the normal of the substrate surface. (5) On (111)B GaP, in addition to the result of (4), twinning about [21] was observed.

Sharp optical emission from CuInSe2 thin films grown by molecular beam epitaxy

Optical properties of CuInSe2 (CIS) films grown on (001) GaAs by molecular beam epitaxy (MBE) have been investigated by means of low temperature photoluminescence (PL) spectroscopy. Distinct emission lines including a bandedge emission were observed reproducibly from Cu-rich films, indicating high crystalline quality. Such well-defined PL spectra have made possible the extensive characterization of radiative recombination processes through the intrinsic defects in this material; some of the emission lines were attributed to phonon replicas with a phonon energy of 28–29 meV for the first time. PL spectra were found to be very sensitive to the MBE growth parameters such as substrate temperature, suggesting dominant defects in CIS epitaxial films can be controlled by varying the growth conditions.

Molecular Beam Epitaxial Growth and Properties of CuInSe2

CuInSe2 (CIS) films with Cu/In ratios (γ) ranging from 0.81 to 1.81 have been grown by molecular beam epitaxy on (001)-oriented GaAs substrates at a substrate temperature of Ts=450°C. It is found that Cu-rich films tend to become Se-poor, and In-rich films tend to become Se-rich. X-ray diffraction patterns obtained from these films have shown the peaks with respect to CIS {n00} planes, clearly indicating epitaxial growth. Optical properties of the CIS films have been characterized by means of photoluminescence (PL) spectroscopy at 2 K. Many distinct emission lines including a band edge emission were present on PL spectra obtained from Cu-rich films. A broad emission (λ~1.45 µm) appeared at γ=1.04, then became dominant with further decreasing γ.

Photoluminescence properties of CuInSe2 grown by molecular beam epitaxy

Abstract Photoluminescence (PL) properties of CuInSe 2 thin films with Cu/In ratio ranging from 0.81 to 1.81 grown by molecular beam epitaxy have been investigated for photovoltaic applications. The PL spectra of Cu-rich CuInSe 2 epitaxial films unlike those of polycrystalline CuInSe 2 showed well-defined emission lines, suggesting that high quality CuInSe 2 epitaxial films have been grown. Such fine PL spectra made the identification possible of phono replicas, in other words, the separation of such phonon replicas from substantive emmissions. PL properties are found to be very sensitive to the growth parameters such as Cu/In ratio and substrate temperature. A broad peak at λ ∼ 1.45 μm becomes dominant in In-rich films, and excitation power dependence of such a broad emission indicated a pair-type radiative recombination, most likely the emission due to donor-acceptor pair or their complex.

Epitaxial Growth of GaN1-xPx (x \lesssim0.04) on Sapphire Substrates

Gallium nitride phosphide (GaN1-xPx) was epitaxially deposited on (0001) sapphire substrates by the vapor phase reaction of the Ga-NH3-PCl3-N2 system. The growth rate was 0.80 µm/hr at 1100°C and decreased with decreasing growth temperature. Composition x increased with decreasing growth temperature. The maximum composition x obtained was about 0.04 at 1050°C.

Epitaxial Growth of Mo Single Crystal on Sapphire by H2 Reduction of MoO3 and Characterization by Reflection High-Energy Electron Diffraction

Mo depositions on sapphire ( Al2O3) were effected by H2 reduction of MoO3, and the crystallinity of the films was characterized by reflection high-energy electron diffraction (RHEED). In the case of growth on the (102) Al2O3 substrates, single-crystal epitaxial growth of (001) Mo was realized. On (0001) Al2O3, single-crystal Mo was not obtained; Mo deposited on (0001) Al2O3 was composed of three sets of (110)-oriented crystallites. To obtain Debye-Scherrer ring-free Mo films whose RHEED patterns did not include arcs, growth temperatures of 890 and 920° C were required in growths on (102) and (0001) Al2O3 substrates, respectively.

(112)-Oriented growth of CuInSe2 on (001) Mo single-crystal substrates

CuInSe2 depositions on (001) Mo single-crystal substrates were achieved by the Se(CH3)2-halogen transport method and the crystallinity of the layers were characterized by reflection high-energy electron diffraction. On the (001) Mo substrates, {001} CuInSe2 was not obtained; CuInSe2 deposited on (001) Mo was composed of four sets of (112)-oriented crystallites which were rotated every 90° about the substrate surface normal. To explain the appearance of the (112) plane, a minimum lattice-mismatch criterion taking into consideration the fact that Mo has a bcc structure was proposed. To obtain Debye-Scherrer-ring-free CuInSe2 films, introducing Br2 to transport In and Cu before introducing Se(CH3)2 was essential.