S. Minagawa

NITRIDATION PROCESS OF SAPPHIRE SUBSTRATE SURFACE AND ITS EFFECT ON THE GROWTH OF GAN

The nitridated layer formed on a (0001) sapphire (α‐Al2O3) substrate surface by heating at 1050 °C in ammonia (NH3) gas was analyzed by x‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscope (TEM) and energy dispersive x‐ray spectrometry (EDX). Their influence on the growth of GaN in the combined usage of initial nitridation and successive deposition of a buffer layer was examined by AFM observations. The intensity of the N1s nitrogen peak in the XPS rapidly increased with nitridation time, reaching saturation in a few minutes, and then continued to increase gradually. This change was found to correspond to morphological change revealed by AFM observations, that is, from a flat nitridated layer to high‐density (109–1010 cm−2) nitridated protrusions. TEM observations and EDX measurements showed that the nitridation forms an amorphous layer consisting of AlNxO1−x. The flat nitridated layer, when combined with a buffer layer, favors two‐dimensional growth of a...

Crystalline and electronic energy structure of OMVPE-grown AlGaInP/GaAs

Abstract The crystalline and electronic energy structure of AlGaInP/GaAs grown by organometallic vapor phase epitaxy (OMVPE) is investigated using transmission electron microscopy (TEM) and electroreflectance (ER), as well as photoluminescence (PL) and Raman scattering measurements. In TEM observation, sharp superstructure spots at the h+ 1 2 , k− 1 2 , l± 1 2 position, corresponding to CuPt type structure, are present in the (110) diffraction pattern. Based on this observation, the relationship between the bond and the ordered structure configuration on 9001) growth surface is discussed. It is also found by photoluminescence and Raman scattering measurements that the GaInP grown on (111)B is in a disordered state. Photoluminescence measurement for AlGaInP grown under various conditions shows that an ordered structure exists not only in GaInP but throughout the entire compositional range of the AlGaInP/GaAs. The electroreflectance spectrum shows anomalous structures specific to OMVPE-grown GaInP. The structures around 2.2 and 2.4 eV suggest that there exist additional interband transition edges caused possibly by zone-folding from the L point to the Γ point.

Electroreflectance study of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy

We have measured the electroreflectance spectra of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy. As a result, it has been found that there exist anomalous structures in the region of the E0 and E1 band edges of this material. These anomalous structures are closely related to the recently reported ordered phase in this alloy, since these structures have never been observed with disordered Ga0.5In0.5P alloys such as bulk crystals and epitaxial layers grown by liquid phase epitaxy.

Effect of cap layer and cooling atmosphere on the hole concentration of p(Zn)-AlGaInP grown by organometallic vapor phase epitaxy

Abstract Hole concentration of p(Zn)-(Al 0.7 Ga 0.3 ) 0.5 In 0.5 P grown by organometallic vapor phase epitaxy is influenced by cooling atmospheres and capping layers. A high hole concentration is obtained when an epitaxial layer is cooled in a hydrogen stream, while cooling in a phosphine- or arsine-containing hydrogen atmosphere reduces hole concentration in this order. A cap layer, n- or p-GaAs is useful in maintaining a high hole concentration. The zinc acceptors in a layer with a low hole concentration can quickly be reactivated by annealing in hydrogen.

Transverse‐mode‐stabilized ridge stripe AlGaInP semiconductor lasers incorporating a thin GaAs etch‐stop layer

Transverse‐mode‐stabilized ridge stripe AlGaInP semiconductor lasers fabricated using a thin GaAs layer as an etch stop are reproducibly realized. The ridge stripe structure is fabricated utilizing the large difference in etching rates between GaAs/AlGaAs and AlGaInP layers. As a result, the thickness control of the cladding layer adjacent to light absorbing layers is significantly improved. Results show that the GaAs layer is effective as an etch‐stop layer even if the thickness is only 1–2 nm. The total internal loss of the lasers is estimated to be about 20 cm−1 and loss due to the insertion of the GaAs layer is almost negligible. A threshold current of about 50 mA and a stable fundamental transverse mode up to an output power of about 10 mW is attained at room temperature under cw operation. Similar results were obtained when an AlGaAs layer was used instead of GaAs.

The energy band alignment of Xc, Γc, and Γv points in (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP heterostructures

Better carrier confinement in 0.6-μm-band laser diodes can be achieved by incorporating an AlInP layer into the (Al0.7Ga0.3)0.5In0.5P cladding layers. The effectiveness of this heterostructure, though, cannot be analyzed without detailed knowledge of the energy band alignment at the Xc, Γc, and Γv band extrema. We conducted photoluminescence and photoreflectance measurements at 12–100 K on (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP heterostructures (x=0.47–0.61) free from long-range ordering, and analyzed the results to obtain basic data on the alignment scheme. In these measurements we observed the Γc to Γv and the Xc to Γv transitions in bulk Al0.53In0.47P and (Al0.7Ga0.3)0.5In0.5P alloys, the AlxIn1−xP Xc to (Al0.7Ga0.3)0.5In0.5P Γv transition in (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP superlattices, and the Xc to Γv and to the Γc to Γv transitions in 20-nm-wide AlxIn1−xP layers in (AlyGa1−y)0.5In0.5P/AlxIn1−xP/(AlyGa1−y)0.5In0.5P double heterostructures (x=0.33–0.39, y=0.7–1.0). We found that the energy level of Xc in A...

Heavy doping of silicon into Ga0.5In0.5P at low temperatures in organometallic vapor phase epitaxy

High concentration doping of silicon into Ga0.5In0.5P layers using disilane as the doping precursor in organometallic vapor phase epitaxy is performed at growth temperatures between 620 and 700°C. The electron concentration changes linearly with disilane flow rate, reaching a maximum at 1 × 1019 cm−3 and staturates thereafter, while the silicon concentration keeps increasing. Heavy doping raises the photoluminescence (PL) peak energy to 1.95 eV. The increment is 120 meV at lower growth temperatures on (100) substrates, but it remains 40 meV on (511)A. The former is due to the combined effect of electron concentration and atomic disordering, whereas the latter is due to electronic effects only.

Silicon shadow mask MOVPE for in-plane thickness control of InGaAsPInP structures

A new epitaxial growth technique is proposed for local thickness modulation in simultaneously grown layers to achieve thickness-tapered waveguide structures. This technique uses a comb-shaped silicon shadow mask placed just above the substrate during metalorganic vapor phase epitaxy (MOVPE). Smoothly tapered InP and InGaAs layers were obtained with a maximum in-plane thickness reduction ratio of over 8. Tapered multiple quantum well layers exhibited clear blue-shift in quantum energy and sufficient photoluminescence in areas with uniform thickness, which were equivalent to those grown by normal MOVPE without the shadow mask.

LASING OPERATION UP TO 200 K IN THE WAVELENGTH RANGE OF 570-590 NM BY GAINP/ALGAINP DOUBLE-HETEROSTRUCTURE LASER DIODES ON GAASP SUBSTRATES

Short‐wavelength stimulated emission from a GaInP/AlGaInP double‐heterostructure (DH) grown on GaAs0.6P0.4 substrates, where lattice‐matched Ga0.7In0.3P is the active layer with Γ band‐gap energy beyond 2.1 eV is investigated. Laser oscillation is attained at a wavelength below 590 nm. This shows that the DH attains sufficient carrier confinement for lasing even though the minimum Γ band‐gap energy is close to that in the X band. By applying high‐reflectivity coating on both facets of the cavity to decrease the optical mirror loss, we achieve lasing operation by the DH devices under pulsed current injection up to 200 K. The device exhibits threshold currents of 115 mA at 77 K and 380 mA at 200 K, and an output power level up to 0.3 mW. The oscillation wavelength is 577 nm at 77 K and 588 nm at 200 K when the current is injected at 1.2 times the threshold.

Uniform p‐type impurity‐doped multiquantum well AlGaInP semiconductor lasers with a lasing wavelength of 633 nm at 20 °C

Impurity doping into a GaInP/AlGaInP multiquantum well (MQW) active layer is applied to suppress the occurrence of the ordered structure of column III elements. Calculation of the quantized energy level in an ordered and disordered GaInP quantum well (QW) shows that uniform p‐type impurity doping into a MQW structure is more effective than modulation doping for shortening the lasing wavelength. The lasing wavelength of p‐doped MQW lasers with a 3‐nm‐thick GaInP QW can be shortened to 633.2 nm at an output power of 2 mW at 20 °C. A maximum lasing temperature of 46 °C for a 630 nm band AlGaInP MQW laser with a cavity length of 450 μm is obtained.