Takatosi Nakanisi

Room‐temperature cw operation of InGaP/InGaAlP visible light laser diodes on GaAs substrates grown by metalorganic chemical vapor deposition

Room‐temperature cw operation for InGaP/InGaAlP double heterostructure (DH) laser diodes on GaAs substrates was achieved for the first time. The DH wafers were grown by low‐pressure metalorganic chemical vapor deposition using methyl metalorganics. A lasing wavelength of 679 nm and a threshold current of 109 mA at 24 °C were obtained for an inner stripe structure laser diode with a 250‐μm‐long and 7‐μm stripe geometry. The laser operated at up to 51 °C. The characteristic temperature T0 was 87 K at around room temperature. The lowest threshold current density, 5.0 kA/cm2, was obtained with a 20‐μm stripe width laser diode under room‐temperature pulsed operation.

Growth of high-quality inGaAIP epilayers by MOCVD using methyl metalorganics and their application to visible semiconductors lasers

In an attempt to obtain high-quality In0.5(Ga1−xA1x) 0.5P epilayers on GaAs substrates for visible semiconductor la applications, effects of growth procedure and conditions (growth temperature, V/III ratio, etc.) were investigated by low-pressure MOCVD technique, using trimethyl metalorganics. It was found that fast gas compositional switching, growth temperatures as high as 700°C and V/III ratios larger than 200 were prerequisite to obtaining high-quality epilayers. Low-resistivity layers with resistivity less than 0.2 Ω cm were readily obtained with both Se and Zn doping for x<0.5. Room temperature CW operation of an In0.5Ga0.5P/In0.25A10.25P DH laser was achieved, with a threshold current density of 5.0 kA/cm2, using DH wafers grown under optimized growth conditions.

Band discontinuity for GaAs/AlGaAs heterojunction determined by C‐V profiling technique

The band discontinuity has been determined for a GaAs/AlGaAs heterojunction prepared by molecular beam epitaxy. The conduction band‐discontinuity ΔEc and the valence‐band discontinuity ΔEv were independently obtained by the C‐V profiling technique, taking into account a correction for the interface charge density. The simulation was employed to confirm the reliability of the obtained band discontinuity. The ΔEc dependence on both the Al composition of the AlGaAs layer and the heterojunction structure (AlGaAs on GaAs, or GaAs on AlGaAs) was examined. We found that ΔEc and ΔEv were determined to be 62 and 38% of the band‐gap discontinuity ΔEg, being independent of the structure.

Growth of high-purity GaAs epilayers by MOCVD and their applications to microwave MESFET's

Abstract In an attempt to obtain high-purity GaAs epilayers for microwave device applications by a (CH3)3Ga/AsH3 MOCVD technique, effects of starting materials quality and growth parameters were investigated. It was found that the epilayer quality is mainly limited by the (CH3)3Ga purity. Analyses using flameless atomic absorption spectrophotometry showed that the (CH3)3Ga sources contained a large amount of Si as compared with other metallic impurities. By using refined (CH3)3Ga with reduced impurity contents and by optimizing growth conditions, a layer with an electron mobility at 77 K of 139,000 cm2/V · s at an electron concentration of 3.7 × 1014/cm3 was obtained. For low-noise MESFET applications, n- − n − n+ epilayers were grown successively on semi-insulating GaAs substrates. Improvement of the layer purity has made it possible to grow n- buffer layers thick enough to avoid substrate effects. Al gate MESFETs fabricated with gate dimensions of 0.5 μm × 300 μm showed a noise figure of 2.0 dB with an associated gain of 8.2 dB, and a maximum optimized gain of 12 dB at 12 GHz.

The growth and characterization of high quality MOVPE GaAs and GaAlAs

Abstract High-purity GaAs and GaAlAs epilayers have only been grown by MOVPE very recently. They are successfully used for the layers of microwave MESFETs and semiconductor lasers. This paper briefly reviews the recent progress in the area of high-quality epitaxial growth of GaAs and GaAlAs. Then, the important problems which remain unsolved are discussed. Electrical and optical properties of epilayers are presented with reference to the starting materials quality, growth conditions, and impurity doping. The dominant residual impurities in GaAs and GaAlAa are discussed. Finally the important role of deep levels on the layer quality is pointed out.

Growth temperature dependent atomic arrangements and their role on band-gap of InGaAlP alloys grown by MOCVD

Detailed observation of atomic arrangement in In0.5(Ga1−xAlx)0.5P(0⩽x⩽1) grown by MOCVD with a wide range of growth temperatures Tg (570–770° C) was carried out using electron diffraction and high resolution transmission electron microscopy. A correlation between the atomic arrangement and band-gap energy was studied by photoluminescence and photoacoustic spectroscopy. For Tg≲760° C, the epitaxial layers have ordered structures. For Tg≳770° C, the ordering disappear. Shifts in the band-gap depend on the density of the ordered layers for x≲0.5. For x≳0.5, the band-gap is not affected by the ordering.

A study of p-type doping for AlGaInP grown by low-pressure MOCVD

Abstract Doping characteristics for Mg (and Zn) in (Al x Ga 1− x ) 0.5 In 0.5 P have been studied with a view towards applying Mg (or Zn) doped AlInP to DH lasers. The solubility limits for the dopants decreased with increasing Al composition. The maximum hole concentration of Zn doped AlInP was at most 2×10 17 cm −3 , which is too low for practical use in DH lasers. The solubility limits for Mg were several times higher than those for Zn. The maximum hole concentration of Mg doped AlInP was 1×10 18 cm −3 . The Mg incorporation was considered to be limited by Mg revaporization from the growth surface. The Mg incorpolation at a constant doping-source introduction in AlGaInP increased with increasing Al composition. The proportion of electrically active Mg to total incorpolated Mg (electrical activity) does not change markedly with Al composition. The Mg electrical activity was quite low even at low doping levels.

Effects of the Growth Conditions on Deep Level Concentration in MOCVD GaAs

Growth parameter dependence of the concentration of a dominant deep level (Ec-0.84 eV) in undoped and S-doped MOCVD grown GaAs has been studied by DLTS. Considerable attention has been paid to the analysis of DLTS signal in order to obtain the true concentration from the experimental data. It has been found that the concentration of 0.84 eV level is proportional to ([AsH3]/[TMG])1/4. It increases with growth temperature, and decreases with increase in the concentration of doped S. The mole ratio dependence of the 0.84 eV level concentration suggests that the dominant deep level in GaAs is closely related to a Ga vacancy.

Effects of the Growth Temperature and Substrate Orientation on the Incorporation of Si, Ge and Sn into Vapour Epitaxial GaAs

Undoped and doped epitaxial layers with carrier concentrations from 1015 to 1017 cm-3 were grown by using the AsCl3/Ga/GaAs/H2 transport system. Electrical and photoluminescence measurements showed that Si, Ge and Sn were incorporated amphoterically from the dopant source GaAs into epitaxial layers. Evidence is given indicating that the major electrically active impurity in undoped layer is Si. The growth temperature dependence of the impurity incorporation is well described by the Arrhenius relation. The activation energies Eis vary systematically with the impurity species. They decrease in the order of Si>Ge>Sn. Also Eis vary with the substrate orientation, decreasing in the order of (100)>(111)B>(110). These dependences can be described satisfactorily in terms of the kinetic reactions between the impurity and the growing surface.

Photothermal ionization identification of sulfur donors in GaAs

Photothermal ionization data for undoped and S‐doped epitaxial GaAs grown by metalorganic chemical vapor deposition (MOCVD) are presented which permit the positive identification of the S donor. This identification is unambiguous because S is not a significant residual impurity in the undoped MOCVD GaAs used for these measurements. Implications of the new identification for the importance of S as a residual donor in epitaxial GaAs prepared by various other growth techniques.