Y. Koide

Effects of ain buffer layer on crystallographic structure and on electrical and optical properties of GaN and Ga1−xAlxN (0 < x ≦ 0.4) films grown on sapphire substrate by MOVPE

Abstract GaN and Ga 1−x Al x N (0 x ≦ 0.4) films grown by MOVPE on (0001) sapphire substrate are found to consist of many mosaic crystallites with various orientations. By preceding deposition of a thin AIN buffer layer, the microscopic fluctuation in crystallite orientation can be considerably reduced and the crystalline quality of the film is remarkably improved. Both the thickness and the deposition temperature of the AIN layer are found to be optimal as a buffer layer to convey the information of the substrate such as the crystallographic orientation and to relax the strain in this heteroepitaxial growth. The essential role of the AIN buffer layer is thought to be the supply of nucleation centers having the same orientation as the substrate and the promotion of lateral growth of the film due to the decrease in interfacial free energy between the film and the substrate.

Energy band‐gap bowing parameter in an AlxGa1−x N alloy

Optical measurements are performed near the fundamental absorption edge for single‐crystal AlxGa1−x N epitaxial layers in the composition range of 0≤x≤0.4. The dependence of the energy band gap on composition is found to deviate downwards from linearity, the bowing parameter being b=1.0±0.3 eV. The origin of the large bowing is discussed in terms of the pseudopotential of Al and Ga based on the pseudopotential of the Heine–Abarenkov type. With increasing x the absorption edges broaden, which is attributed to the increase of the compositional nonuniformity.

Solid‐phase reactions and crystallographic structures in Zr/Si systems

Solid‐phase reactions and crystallographic structures in the interfacial region of Zr/(100)Si systems, which is closely related to the specific contact resistivity, have been investigated by x‐ray diffraction, Auger electron spectroscopy and cross‐sectional high‐resolution transmission electron microscopy. As‐grown Zr films are in an amorphous phase including crystallites. The Zr film on silicon annealed at a temperature of 420 °C for 30 min has a bilayer structure. The upper layer is a crystalline α‐Zr layer with a (0001) fibrous structure and the lower layer is an amorphous zirconium silicide layer. The formation of the amorphous silicide layer is considered to result from the diffusion of Si atoms from the substrate into the Zr film and to play a major role in a low contact resistivity of 4×10−8 Ω cm2 achieved in this system. By annealing above 560 °C, which brings about an increase in contact resistivity, the crystalline Zr layer with the fibrous structure is changed to an amorphous silicide throughou...

Edge emission of AlxGa1−xN

Abstract The photoluminesence in the edge emission region of Al x Ga 1−x N> (0 ≦ x ≦ 0.24) has been studied. The compositional dependence of the band gap was studied and the bowing parameter was determined: b = 0.98 eV . With increasing x the edge emission peak broadens, explanation of the mechanism of which has been attempted.

Initial stage of growth of Ge on (100)Si by gas source molecular beam epitaxy using GeH4

The growth process in the initial stage of growth of Ge on (100)Si substrates by gas source molecular beam epitaxy using GeH4 has been investigated by in-situ reflection high-energy electron diffraction (RHEED) observation. It has been found that the growth mode is the Stranski-Krastanov type, and that the predominant facet of Ge islands is {811} planes at the first step of the island growth but changes to {311} planes with the growth.

Growth processes in the initial stages of deposition of Ge films on (100)Si surfaces by GeH4 source molecular beam epitaxy

Abstract Growth process in the initial stages of deposition of Ge films on (100)Si surfaces by GeH 4 source MBE has been studied by in-situ reflection high energy electron diffraction (RHEED) observation. The growth mode is of the Stranski-Krastanov type, and the strained monolayer overgrowth on the substrate surfaces takes place over the observed temperature range of 300–600 C. The growth behavior in the nucleation and island growth stages is found to change strikingly near 500 ° C. The activation energy of the growth rate above 500 ° C (0.24 eV) is 10 times as large as than that below 500 ° C (0.023 eV). In spite of these marked differences, the predominant facets of the growing islands is {8111} Ge planes initially and this changes to {311} Ge eventually with growth in the two temperature ranges. Half-order streaks associated with a (2×1) structure are observed to incline to 〈811〉 Ge in the diffraction patterns. This analysis gives information on the atomic arrangement of {811} Ge .

EFFECTS OF OXIDATION CONDITIONS ON ELECTRICAL PROPERTIES OF SIC-SIO2 INTERFACES

Electrical properties of metal‐oxide‐semiconductor (MOS) devices fabricated on 3C‐SiC single crystalline films on (100)Si substrates have been examined by capacitance‐voltage method and deep level transient spectroscopy. The electrical properties such as carrier concentration, interface states, fixed oxide charge and deep traps are strongly related to the oxidation ambient and temperature. It has been found that the interface state density of the order of 1010 cm−2 eV−1 can be achieved by wet oxidation at 1000 °C. The influence of preferential oxidation of antiphase grain boundaries is considerable on the carrier concentration and the interface state density in the case of wet oxidation. From a practical point of view, the wet oxidation is concluded to be superior to the dry oxidation because of the lower densities of fixed oxide charge, interface states, and deep traps.

Mechanisms of silicon oxidation at low temperatures by microwave-excited O2 gas and O2-N2 mixed gas

Mechanisms are discussed on the enhancement of silicon oxidation at low temperatures by microwave excitation of O2 gas and on the further increase by that of O2 ‐N2 mixed gas. The activation energy of parabolic rate constants for the oxidation by excited pure O2 gas is 1.15 eV. This value, being almost the same as that in thermal oxidation, indicates that the oxidizing species is O2 molecules. The enhancement of oxidation is interpreted as a consequence of an increase in the O2 adsorption energy on SiO2 surfaces. For the oxidation by O2 ‐N2 mixed gas, on the other hand, there exist two parallel oxidation processes: one with the excited O2 gas and the other with excited N2 gas. The activation energy for the latter oxidation process is 0.49 eV, which indicates that the oxidizing species is O atoms. We also observed an abnormally high oxidation rate in the range of small O2 /N2 ratios.

Observation of an ordered structure in the initial stage of Ge/Si heteroepitaxial growth

An ordered structure with the double periodicity in a 〈111〉 direction has been found by in situ reflection high‐energy electron diffraction observation in the initial stage of Ge films grown on (100)Si and (811)Si substrate surfaces by GeH4 gas source molecular beam epitaxy. The ordered structure is formed on {111} planes parallel to the side planes of 〈011〉 steps on {811} facets of Ge growing islands on both substrates. The formation is observed at substrate temperatures of 300–700 °C and is considered to result from solid phase reactions at the interfaces during growth.

Solid phase reaction and electrical properties in Zr/Si system

The specific contact resistivity and the Schottky barrier height in the Zr/Si system have been measured as a function of annealing temperature. The specific contact resistivity decreases with increasing annealing temperature and a minimum value of 4×10−8 Ω cm2 is obtained after annealing at 420 °C in a vacuum, which is about two orders of magnitude lower than that of the Al (1.5% Si)/n+‐Si system. The formation of ZrSi2 is observed at annealing temperatures above 350 °C, which can be considered to be related to the lowering of contact resistance. The Schottky barrier heights of as‐grown Zr films are 0.61 eV for p‐type Si and 0.52 eV for n‐type Si.