Shun–ichi Gonda

New III-V Compound Semiconductors TlInGaP for 0.9 μm to over 10 μm Wavelength Range Laser Diodes and Their First Successful Growth

New III–V compound semiconductors TlInGaP (thallium indium gallium phosphide) lattice-matched to InP are proposed for 0.9 µm to over 10 µm wavelength range laser diodes and their first successful growth is reported by gas-source molecular beam epitaxy. A type-I band lineup and a larger band discontinuity in the conduction band than in the valence band are expected for their heterostructures. They also have the potential to exhibit a temperature-independent band-gap energy (wavelength), which is promising for the fabrication of lasers that can be used in wavelength division multiplexing (WDM) optical fiber communication. Grown layers exhibit (2×4) surface reconstruction and have mirror-like surfaces. Phase separation is not observed in this material system by X-ray diffraction measurement.

GaN-Rich Side of GaNAs Grown by Gas Source Molecular Beam Epitaxy

A large variation in wavelength from the ultraviolet to longer than 2 µm could be achieved in the GaN-rich side of the GaN1-xAsx alloy due to the large bowing of bandgap energy. Layers of GaN1-xAsx are grown on (0001) sapphire substrates by electron cyclotron resonance molecular beam epitaxy (ECR-MBE) using an ion-removed ECR radical cell after the growth of GaN buffer layers. During the growth of GaN1-xAsx layers, a streaky reflection high-energy electron diffraction (RHEED) pattern was observed. The excitonic photoluminescence (PL) peak from the GaN-rich side of the GaN1-xAsx layer shows a large red shift as the As content changes. When an As content of up to x=0.009 is attained, a bandgap bowing parameter of 19.6 eV is experimentally obtained. Such a large value of the bowing parameter is promising for applications to optical devices operating over wide range of wavelength.

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.

Vertical Quantum Confinement Effect on Optical Properties of Strain-Induced Quantum Dots Self-Formed in GaP/InP Short-Period Superlattices

Optical properties of multilayer quantum dots (MQDs) self-formed in the GaP/InP short period superlattice (SL)/InGaP multilayer structures are investigated by changing the SL period (P) and InGaP barrier thickness (B). By decreasing P, photoluminescence (PL) peak energy is shifted toward higher energy due to the quantum size effect along the growth direction (vertical direction). PL linewidth broadening with temperature is reduced by decreasing P and B. This improvement is attributed to the reduction of potential distribution among quantum dots (QDs) and the enhancement of quantum confinement along the vertical direction, and to the enhancement of quantum confinement due to the vertical coupling effect between QDs. Stokes shift for the MQDs structure is observed to be small. Very small temperature variation of PL peak energy is observed in these MQDs, which originates from the existence of the multiaxial strains among the MQDs. Electroluminescence (EL) spectra show split peaks corresponding to the subbands of QDs on increasing injection current.

Effect of substrate temperature on composition ratio x in molecular‐beam‐epitaxial GaAs1−xPx

GaAs1−xPx crystals were grown by molecular‐beam epitaxy with parametric variation of substrate temperature Ts (540–580 °C) and of the ratio of beam intensity of P to that of As (2–11). The rate of decrease of composition ratio x with temperature, −dx/dTs, is 0.003 °C−1 for all ratios of beam intensity. The sticking coefficient of P is found to vary inversely proportional to the substrate temperature in this temperature range. This fact indicates the possibility of writing two‐dimensional patterns on the surface by a partial temperature rise.

CHARACTERIZATION AND SUBSTRATE-TEMPERATURE DEPENDENCE OF CRYSTALLINE STATE OF GaAs GROWN BY MOLECULAR BEAM EPITAXY.

Thin films of GaAs single crystal were prepared successfully on GaAs (100) substrates by molecular beam epitaxy using an ultrahigh vacuum system with effusion cells and a quadrupole mass analyzer. The dependence of the quality of the GaAs film on the substrate temperature, Ts, was investigated in detail at a constant Ga and As2 arrival rate. The epitaxial process was studied in situ with a high energy electron diffraction (HEED) system. The analysis and characterization of the prepared GaAs films were made with a scanning electron microscope, an ion microprobe analyzer, an ESCA photoelectron spectrometer and photoluminescence measurements. These measurements indicate that GaAs films grown at 480\lesssimTs\lesssim530°C by molecular beam epitaxy have smooth surface and nearly the same quality as bulk crystal.

Nitrogen doping into GaAs1−xPx using ionized beam in molecular beam epitaxy

Abstract A new method of nitrogen doping into GaAs 1− x P x was attempted using the ionized beam in molecular beam epitaxy (MBE). With the ionization system attached to MBE system, the ionized nitrogen beam was supplied onto the substrate during MBE. Nitrogen doping of more than 10 18 cm -3 was successfully made without disturbing the high crystallographic quality of the epitaxial layer. Photoluminescence measurements show that the nitrogen atoms introduced into the epitaxial layer act as isoelectronic luminescence centers. The effective sticking coefficient of ionized nitrogen for GaAs 1− x P x at 580°C is estimated as the order of 0.01.

MOLECULAR BEAM EPITAXIAL GROWTH OF InP.

InP thin crystalline films were grown on (100)-oriented GaAs by molecular beam epitaxy (MBE) and evaluated by RHEED, SEM and IMA. Thin films with high crystalline quality were obtained when the substrate temperature was about 240°C and temperatures of In and P cells were 840~880°C and 370~400°C, respectively. Furthermore, Sn atoms were easily doped into InP during MBE growth, and the surface morphology of InP was greatly improved by Sn doping.

Photoluminescence Wavelength Dependence on Layer Structure of GaP/AlP Modulated Superlattices.

In the (GaP)m 1(AlP)n 1(GaP)m 2(AlP)n 2 (m=m1+m2, n=n1+n2, m1≥m2, n1≥n2) modulated superlattices (SLs) grown on (001) GaP substrates by gas-source molecular beam epitaxy, a blue shift of 4.2 K photoluminescence (PL) peak is observed with decreasing the wide periods of (m1+n1). It is suggested that holes and electrons are localized in the wide GaP (m1) and AlP (n1) layers, respectively, and that the PL peak wavelength is mainly determined by the wide SL periods of (m1+n1). This suggestion is supported by the observed PL peak wavelengths for the {(GaP)11(AlP)3}j {(GaP)2(AlP)2}2 and (GaP)5(AlP)5{(GaP)2(AlP)2}k modulated SLs, where the wavelengths are almost independent of j and k.

Improved Optical Properties of Strain-Induced Quantum Dots Self-Formed in GaP/InP Short-Period Superlattices.

Optical properties of multilayer quantum dots (MQDs) self-formed in the GaP/InP short-period superlattice (SL)/InGaP multilayer structures are investigated as a function of InGaP barrier thickness (B). Photoluminescence (PL) linewidth broadening with temperature is improved and tends to reduce by decreasing B. This is attributed to the vertical coupling effect between QDs and their vertical alignment. Temperature variation of PL properties shows the exciton behavior. At low temperatures, emissions from both bound exciton and free exciton appear under the weak excitation density condition. Integrated PL intensity is quite stable up to 120 K.