Masao Mashita

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.

Donor Levels in Si-Doped AlGaAs Grown by MBE

Donor levels of MBE-grown Si-doped AlxGa1-xAs have been characterized by a combination of the C-V method and capacitance and current transient spectroscopy. Although most electrons are supplied by so-called DX centers in the AlAs mole fraction (x) range of 0.3~0.7 in this material, it is found that a small amount of shallow donors are still present. The concentrations of the DX center and the shallow donor are determined in detail as a function of AlAs mole fraction and Si doping level. The activation energy obtained by the Hall effect measurement is discussed in association with these data.

The pyrolysis temperature of triethylgallium in the presence of arsine of trimethylaluminum

Abstract The pyrolysis of triethylgallium (TEG) in H 2 has been investigated using a quadrupole mass spectrometer in a low-pressure (0.1–2.0 kPa) OMVPE growth reactor. The pyrolysis temperature of TEG is influenced by the addition of arsine (AsH 3 ) or trimethylaluminum (TMA). The addition of arsine lowers the TEG pyrolysis temperature and results in the formation of ethane (C 2 H 6 ) and ethylarsines ((C 2 H 5 ) n AsH 3−n , n = 1−3). These poducts indicate the generation of ethyl radicals a nd the reaction between ethyl radicals and arsine. The arsine reacts with the ethyl radical and hence promotes the decomposition of TEG. On the other hand, the addition of TMA to TEG raises the TEG pyrolysis temperature. Only mixing TEG and TMA at room temperature was found to produce methyldiethylgallium (MeEt 2 Ga) and dimethylethylgallium (Me 2 EtGa). These products, which show higher pyrolysis temperatures than pure TEG, can explain the higher TEG pyrolysis temperature for TEG mixed with TMA. These mixed alkyls (Me n Et 3−n Ga, n = 1, 2) are produced most likely through the rapid exchange of alkyl groups due to the equilibrium between dimer and monomer.

Silicon doping using disilane in low-pressure OMVPE of GaAs

Abstract Disilane was studied as a doping gas in low-pressure OMVPE of GaAs. The dependence of Si incorporation on growth temperature was investigated over a wide range of growth pressure from 1 to 100 Torr. At low growth pressures (

Structure, Chemical Bonding and These Thermal Stabilities of Diamond-Like Carbon (DLC) Films by RF Magnetron Sputtering

We have deposited diamond-like carbon (DLC) films using RF magnetron sputtering techniques, and investigated structure, chemical bonding of deposited films and these thermal stabilities by Raman spectroscopy and photoelectron spectroscopy. It has been found that the film deposited under typical conditions is amorphous carbon (a-C) with 62% sp2 and 38% sp3 bonds. Ordering of a-C has been observed with an increase in substrate temperature during deposition and similarly observed after postannealing, although the sp3/sp2 ratio in a film does not change even at 900°C. The absence of conversion between sp3 and sp2 bonds indicates that the DLC films have high thermal stabilities.

Molecular Beam Epitaxial Growth of GaAs Using Triethylgallium and Arsine

Undoped GaAs layers were grown by molecular beam epitaxy (MBE) using triethylgallium (TEG) and arsine (AsH3). The electrical properties of grown layers depended on the cracking temperature Tc of AsH3 as well as the AsH3/ TEG ratio. At Tc=750°C, all layers were p-type; the lowest hole concentration was 1.2×1015 cm-3, with a room-temperature mobility of 400 cm2/Vs. At Tc=850°C, p-n conversion occurred as the AsH3/TEG ratio was increased, probably due to compensation between carbon and silicon atoms incorporated.

Elementary process of the thermal decomposition of alkyl gallium

Abstract Bond dissociation energies and activation energies for the elementary processes of thermal decompositions of trimethylgallium (TMG) and triethylgallium (TEG) are determined by means of ab initio molecular orbital calculations. The theoretically obtained reaction rate constant k ( T ) of TMG reproduced quantitatively precise experiments [Jacko and Price, Can. J. Chem. 41 (1963) 1560]: the calculated Arrhenius-type equation of the reaction rate constant of TMG is log 10 k ( T )(s -1 ) = 16.33-[62.2(kcal/mol)/2.303 RT ]. With theoretically calculated rate constants k ( T ), another experiment on the pyrolysis temperature of TEG in MOCVD growth reactors was reproduced qualitatively. These results suggest the thermal decomposition mechanism to be radical decomposition for TMG and molecular elimination for TEG.

Silicon doping from disilane in gas source MBE of GaAs

Disilane (Si2H6) is used as an n-type dopant in gas source molecular beam epitaxial growth of GaAs using triethylgallium (TEG) and AsH3. A linear relationship is obtained between the disilane flow rate and the electron concentration in the range from 1.3×1017 to 1.2×1018 cm-3. The doping efficiency depends on the substrate temperature varied from 480 to 600°C, but only slightly on the AsH3 flow rate. Furthermore, the doping efficiency is observed to be enhanced by a factor of 2.5 when UV laser irradiation is directed normal to the substrate surface.

On the Reaction Mechanism of the Pyrolyses of TMG and TEG in MOCVD Growth Reactors

The differentiation of the plausible mechanism for the thermal decompositions of TMG and TEG taking place in MOCVD growth reactors was carried out by means of the quantum theoretical method using ab initio molecular orbital calculations. It was found that the combination of the radical mechanism for TMG, Ga(CH3)3–Δ·Ga(CH3)2+·CH3, and the molecular mechanism for TEG, Ga(C2H5)3–ΔGaH(C2H5)2+C2H4, explains qualitatively the experiment on the pyrolysis temperatures of TMG and TEG in the MOCVD growth reactor.

UV Absorption Spectra of Adlayers of Trimethylgallium and Arsine

The UV absorption spectra of trimethylgallium (TMG) and arsine adsorbed on silica were investigated. The spectrum of the physisorbed layers of TMG and arsine were similar to the corresponding vapor spectra. On the other hand, the spectrum of the chemisorbed TMG layer was quite different. from that of vapor. Arsine can be chemisorbed on the chemisorbed TMG layer, although it cannot be chemisorbed on silica. The spectrum of the co-chemisorbed layer, consisting of TMG and arsine, was found to extend greatly to longer wavelengths.