Tonao Yuasa

Evidence for the existence of an ordered state in Ga0.5In0.5P grown by metalorganic vapor phase epitaxy and its relation to band‐gap energy

The band‐gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures. Photoluminescence, Raman scattering spectroscopy, transmission electron microscopy, and impurity diffusion were used to investigate this functional relationship. Two pieces of evidence are shown which demonstrate that MOVPE Ga0.5In0.5P epitaxial layers with ‘‘abnormal’’ Eg∼1.85 eV and ‘‘normal’’ Eg∼1.9 eV correspond to an ordered and a random (Ga,In) distribution on column III sublattices, respectively. In an ordered state, a sequence of (110) planes...GaGaInInGaGaInIn...in the [110] direction is the most probable distribution.

Band-Gap Energy Anomaly and Sublattice Ordering in GaInP and AlGaInP Grown by Metalorganic Vapor Phase Epitaxy

The previously reported photoluminescence(PL)-peak-energy anomaly problem for Ga0.5In0.5P grown on GaAs by metalorganic vapor phase epitaxy (MOVPE) was studied in detail. X-ray microprobe analysis, and optical transmission spectra measurements were carried out to examine alloy compositions and band-gap energies (Egs), respectively. The MOVPE growth condition dependence of {1/2, 1/2, 1/2} superlattices (SLs) on the cation sublattice in Ga0.5In0.5P was studied in detail, using transmission electron microscopy. The correlation between the Eg anomaly and the SLs was examined in detail and established. Raman spectra seemed to show zone-folding effects due to the monolayer SL. A similar Eg anomaly was reported for AlGaInP. AlGaInP and AlInP were also found to show the same SLs.

Degradation of (AlGa)As DH lasers due to facet oxidation

The facet deterioration of (AlGa)As DH lasers by aging was analyzed by Auger electron spectroscopy in combination with Ar sputter etching. It was found that oxide was formed on the laser facet during cw operation, and the oxidation degraded lasers not only in long‐term operation but also even at an early stage of operation.

Novel Window-Structure AlGaInP Visible-Light Laser Diodes with Non-Absorbing Facets Fabricated by Utilizing GaInP Natural Superlattice Disordering

Window-structure AlGaInP visible-light ( λL=680 nm) laser diodes (LDs) have been fabricated, for the first time, by utilizing GaInP natural superlattice (NSL) disordering with selective Zn diffusion. The bandgap energy for the active layer near the mirror facets is increased by 70 meV by the NSL disordering. An 80 mW output power in a fundamental transverse-mode has been achieved for the uncoated window LDs under 1 µsec long pulsed operations. The maximum output power density for the window LDs is estimated to be 10 MW/cm2, which is five times higher than that for conventional LDs.

632.7 nm CW Operation (20?C) of AlGaInP Visible Laser Diodes Fabricated on (001) 6? off toward [110] GaAs Substrate

632.7 nm continuous wave operation was achieved at 20°C, by an AlGaInP visible laser diode (LD) with an AlGaInP quaternary active layer fabricated on a (001) GaAs substrate with a misorientation angle of 6° toward the [110] direction. The epitaxial layers for the laser structure are grown by metalorganic vapor phase epitaxy. The lasing wavelength is almost the same as that for He-Ne lasers. Lasing wavelengths for the LDs were also compared with wavelengths for those fabricated on an exact (001) orientation substrate.

Chemically enhanced focused ion beam etching of deep grooves and laser-mirror facets in GaAs under Cl2 gas irradiation using a fine nozzle

Chlorine‐enhanced GaAs maskless etching has been performed with a novel focused ion beam etching (FIBE) system. The system is composed of an air‐locked ultrahigh vacuum chamber, a 30‐keV Ga+ FIB column, and a fine nozzle. The nozzle irradiates a high‐density Cl2 flux on a desired, small area of the sample while retaining a sufficiently low surrounding gas pressure for stable Ga+ FIB emission. Condensed Ga residues, appearing on the etched surface with no Cl2 gas, could be suppressed under Cl2 gas irradiation. Highly chemically enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained by selecting the optimum relationship between scanning time and Cl2 gas pressure. At the maximum yield, a deep groove (about 6 μm) with a smooth surface was obtained by line‐scanning FIBE. The etching was applied to laser‐mirror formation of an AlGaAs laser. A vertical mirror facet, fabricated in advance by a reactive ion beam etching, was trimmed about one micron thick by line‐scanning FIBE. Light o...

CW Optical Power from (Al・Ga)As Double Heterostructure Lasers

CW optical output power was investigated in (AlGa)As double heterostructure lasers. An analysis on CW optical power is presented, and parameters related to device characteristics and heat-sinking are analyzed in order to obtain laser operation with high CW optical power. 20–30 mW CW optical power was obtained routinely from each mirror of lasers with a 15 µm wide stripe and a 250 µm long cavity at a typical operating current of 200 mA. Lasers with a Si heat sink can deliver comparably high CW optical power under proper choice of design parameters. Several lasers delivered 85 mW in CW with a Si heat sink from each mirror at 310 mA, before the catastrophic optical mirror damage occurred. Conditions for long life operation are also discussed.

Composition dependence of photoluminescence of AlxGa1−xAs grown by molecular beam epitaxy

Low‐temperature (∼4 K) photoluminescence of lightly Si‐doped AlxGa1−xAs grown by molecular beam epitaxy has been studied. The defect‐related emissions, due to the defect exciton (d, X) and the defect complex (d), have been identified. The peak energies of these emissions, which are 1.505 eV (d, X) and 1.474 eV (d) for GaAs, have been determined as a function of the mole fraction x ( x<0.45). The energy difference between the donor–bound‐exciton (BE) peak and the defect‐exciton peak is almost constant (∼9 meV). In contrast, the energy difference of the BE peak and the defect‐complex peak increases from 40 meV at x=0 to about 70 meV at x∼0.4. In addition, the ionization energies of carbon and silicon acceptors in AlxGa1−xAs have been determined as a function of x and compared with theoretical calculations.

Short cavity GaAs/AlGaAs multiquantum well lasers by dry etching

A reactive ion beam etching method with Cl2 plasma is applied to fabricate short cavity GaAs/AlGaAs multiquantum well lasers grown by molecular beam epitaxy. Threshold currents as low as 38 mA are achieved for the 20‐μm‐long cavity lasers. The very short cavity lasers show single longitudinal mode operation under pulsed conditions. Cavity length dependence of the threshold current is also investigated for the dry‐etched lasers with cavity lengths varying from 20 to 500 μm.

Characteristics of molecular‐beam epitaxially grown pair‐groove‐substrate GaAs/AlGaAs multiquantum‐well lasers

Growth and device characteristics of an index‐guided GaAs/AlGaAs multiquantum‐well (MQW) laser, called a pair‐groove‐substrate (PGS) MQW laser, are described in detail. The laser structure is fabricated by using single‐step molecular‐beam epitaxy on a (001) GaAs substrate with a pair of etched grooves along the 〈110〉 direction. A mesa between a pair of grooves, where the lasing action occurs, becomes narrow during growth, and the narrow mesa offers lateral waveguiding that stabilizes a fundamental transverse mode. The superior crystalline quality of the mesa top, which is examined by a microprobe photoluminescence technique, serves to lower the lasing threshold currents. The lasers with mesa widths below 2 μm show stable transverse mode operation with a low threshold current of 20 mA, as well as a high external differential quantum efficiency of 68%. The low threshold and high characteristic temperature accomplish a high‐temperature continuous‐wave operation at 153 °C for the lasers mounted on silicon he...