Seiji Kawata

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.

Studies of GaxIn1−xP layers grown by metalorganic vapor phase epitaxy; Effects of V/III ratio and growth temperature

Abstract Properties of GaxIn1−xP grown by metalorganic vapor phase epitaxy at various V/III ratios and growth temperatures were studied by photoluminescence (PL) (300 K, 2 K), X-ray diffraction and Raman scattering measurements. PL peak energy, measured at 300 K, changed from ∼1.90 to ∼1.85 eV, both when V/III was varied from 62 to 412 at 700°C growth temperature and when growth temperature was varied from 750 to 650°C at a fixed V/III ratio of 62, while each GaxIn1−xP layer is lattice-matched t GaAs and has the same composition. The low Pl peak energy (∼1.85eV) was ascribed to the band edge luminescence and not to deep-level related luminiscence. Raman scattering spectra for these samples showed a systematic difference, corresponding only to the PL peak energy difference, indicating that the PL peak energy difference results from an energy band structure difference due to atomic-scale arrangement difference on the group III element sub-lattice. It is suggested that there is a greater degree of atomic-scale clustering on the group III element sub-lattice for samples with low PL peak energy than for samples with “normal” PL peak energy (∼1.9 eV).

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.

P-Type Doping Effects on Band-Gap Energy for Ga0.5In0.5P Grown by Metalorganic Vapor Phase Epitaxy

Photoluminescence properties of Mg- or Zn-doped Ga0.5In0.5P grown by metalorganic vapor phase epitaxy were studied as a function of hole concentration (p). The band-gap energy (Eg) value for Mg- or Zn-doped Ga0.5In0.5P, grown under a condition in which undoped Ga0.5In0.5P shows an anomalously low Eg, showed a steep increase for p~>1×1018 cm-3. This anomalous behavior was attributed to the Mg or Zn diffusion-enhanced randomization of the previously observed naturally formed monolayer {1/2, 1/2, 1/2} superlattices on the column III sublattice.

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.

Large (6?) Off-Angle Effects on Sublattice Ordering and Band-Gap Energy in Ga0.5In0.5P Grown on (001) GaAs Substrates

Effects of a large (6°) misorientation angle of (001) GaAs substrates on the superlattice (SL) formation and the band-gap energy (Eg) for Ga0.5In0.5P were studied. It was found that the [-1/2, 1/2, 1/2] SL formation is strongly enhanced and the [1/2, -1/2, 1/2] SL formation is virtually suppressed, for the case of 6° misorientation towards the [10] direction. In the case of 6° misorientation towards the [110] direction, both SLs were formed, accompanied by significant disorders. The Eg values seemed to correspond well to the degrees of ordering; this is consistent with the previous observation.

Silicon and Selenium Doping Effects on Band-Gap Energy and Sublattice Ordering in Ga0.5In0.5P Grown by Metalorganic Vapor Phase Epitaxy

Effects of n-type dopants Si and Se on band-gap energy (Eg) and on sublattice ordering for Ga0.5In0.5P grown by metalorganic vapor phase epitaxy, under conditions in which Eg shows anomalously low Eg values if the doping is not carried out, were studied by means of photoluminescence and transmission electron microscopy. In contrast to the previously reported p-type doping case, the effects on Eg were interpreted by considering two factors: (i) impurity-doping-induced diorsdering of superlattice (SL), and (ii) Burstein shift.

Nonexistence of Long-Range Order in Ga0.5In0.5P Epitaxial Layers Grown on (111)B and (110)GaAs Substrates

It has been found that Ga0.5In0.5P layers grown at 700°C on (111)B and (110)GaAs substrates do not show {1/2, 1/2, 1/2} superlattice (SL) formation, in contrast to that for the layers grown on (001)GaAs. The band-gap energy for these layers, which show no SL and are lattice-matched to GaAs, was estimated to be 1.918±0.002 eV at room temperature.

Continuous wave operation (77 K) of yellow (583.6 nm) emitting AlGaInP double heterostructure laser diodes

Continuous wave lasing operation with the shortest wavelength for semiconductor lasers was obtained from AlGaInP double heterostructure lasers at 77 K. The structure was grown by metalorganic vapor phase epitaxy. Lasing wavelength was 583.6 nm (yellow). Threshold current was 43 mA (1.9 kA/cm2). Magnesium was adopted as a p‐type dopant, and was proved to be preferable for a high aluminum composition AlGaInP cladding layer.

Transverse Mode Stabilized 670Nm Atgainp Visible-Light Laser Diodes

Transverse mode stabilized AIGaInP visible light laser diodes are described and their high power operations are discussed. The laser structure applied for transverse mode stabilization is a ridge shape self-aligned structure, which is designed taking fabrication reproducibility into consideration. A very thin GaInP etching stopper layer is introduced in order to enable easy and accurate control of the dimensions of the self-aligned structure. Threshold current is about 30-50mA. Over 10mW output power is obtained for LDs with as-cleaved facets. Output power is limited by COD (catastrophic optical damage). COD power level under continuous-wave (cw) operation is estimated to be 1.4-1.7MW/cm2. After facet-coating, a stable fundamental mode operation, up to 20mw (cw), and maximum output power 31mW (cw), which is limited by COD, have been obtained. The lasing wavelength is 670nm.