Miyoko O. Watanabe

Interface properties for GaAs/InGaAlP heterojunctions by the capacitance‐voltage profiling technique

The conduction‐band discontinuity ΔEc and interface charge density σ have been studied for GaAs/In0.5(Ga1−xAlx)0.5P heterojunctions, prepared by metalorganic chemical vapor deposition. The dependences of ΔEc and σ on Al composition x were investigated for x from 0 to 1. The In0.5Al0.5P/ In0.5Ga0.5P heterojunction was also examined. The results suggest that the valence‐band discontinuity ΔEv for GaAs/In0.5(Ga1−xAlx)0.5P is a linear function of x and is larger than ΔEc, being in reasonable agreement with results on the InAlP/InGaP heterojunction. The σ values for GaAs/InGaAlP were found to be one order of magnitude larger than those for GaAs/AlGaAs and InAlP/InGaP heterojunctions.

On the determination of the spatial distribution of deep centers in semiconducting thin films from capacitance transient spectroscopy

It is pointed out that a widely used simple formula may give rise to serious errors in profiling deep level concentrations from capacitance transient experiments. A correction formula is derived based on the space‐charge analysis.

Bonding characterization of BC2N thin films

We have studied the bonding states of BC2N thin films prepared by chemical vapor deposition, one of the new layered BCN compounds. The chemical bonding states of boron, carbon, and nitrogen atoms in the BC2N thin films were investigated by using x‐ray photoelectron spectroscopy to measure chemical shifts of 1s electrons, being compared with those in graphite and hexagonal (h‐) BN. The results exhibited that the thin films had significant B–C and C–N bonds and were clearly different from graphite and h‐BN, indicating that an atomic‐level hybrid of the three elements was synthesized.

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.

Electrical properties of BC2N thin films prepared by chemical vapor deposition

The electrical properties of BC2N thin films have been investigated in terms of the temperature dependence of the resistivity and Hall effect measurements. The BC2N thin films were prepared by chemical vapor deposition from acetonitrile and boron trichloride on polycrystalline Ni and quartz substrates. The experimental results indicated that the BC2N films were p‐type semiconductors on both substrates, with acceptor levels between 7.5 and 23 meV relative to the valence band. The hole mobility on Ni substrates was one order of magnitude higher than that on the quartz substrates, suggesting that the thin film quality is better on Ni substrates than on quartz substrates.

Structural and electrical characterization of BC2N thin films

We have characterized a BC2N compound, one of the new layered BCN compounds. The structural and electrical properties of BC2N thin films, prepared by chemical vapor deposition, have been examined. Microscopic bonding was investigated by chemical shifts in X-ray photoelectron spectroscopy. Binding energies of 1s electrons for B, C and N suggested that an atomic-level hybrid of the three elements was synthesized, implying thai a separation of graphite and hoxagonal BN (h-BN) had not occurred in the films. Transport properties were also investigated by means of temperature dependences of the resistivity and Hall coefficients, and the films were found to be p-type semiconductors.

Se‐related deep levels in InGaAlP

Donor‐related deep levels in Se‐doped In0.5(Ga1−xAlx)0.5P (x=0.0–1.0) have been studied by DLTS, C–V measurement, and photocapacitance techniques. Two donor‐related deep levels were found. The concentrations linearly increased with the donor concentration, and strongly depended on the alloy composition. These levels were found to be dominant donors in the composition range from x=0.3 to x=1.0. They had 0.20 and 0.29 eV activation energies for electron thermal emission, 0.08 and 0.11 eV energies for electron thermal capture, and they had 0.7 and 1.1 eV energies for electron optical emission, respectively. Internally consistent configuration coordinate diagrams were proposed for these levels, suggesting that both levels are similar to DX centers commonly found in n‐AlGaAs.

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.

AsH3 to Ga(CH3)3 Mole Ratio Dependence of Dominant Deep Levels in MOCVD GaAs

Dependence of the 0.8 eV electron trap (so-called EL2) concentration on the As/Ga mole ratio during growth in MOCVD GaAs has been investigated by varying growth temperatures. It has been found that a demarcation exists in the growth temperatures, which divides two regions with different trap concentration-As/Ga mole ratio relationships. The trap concentration increases with the As/Ga mole ratio by the one-fourth power at growth temperatures of 630°C and 660°C, while it increases with the As/Ga mole ratio by the one-half power at 720°C and 740°C. Corresponding with this difference, there is a slight difference in activation energies between the materials grown at the lower temperatures and those grown at the higher temperatures. A possible explanation based on thermodynamic considerations is presented.

Hole generation by icosahedral B12 in high‐dose boron as‐implanted silicon

It was found that a high concentration of holes was generated without any post‐annealing by boron ion implantation into silicon in the high‐dose region of more than 1×1016 cm−2. X‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectrum revealed that B12 icosahedra were created just after implantation. The generation of holes can be explained by the model in which B12 icosahedra act as a double acceptor.