Yasuhito Zohta

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.

Electrical properties of n-type Si layers doped with proton bombardment induced shallow donors

Abstract Sheet Hall coefficients and resistivities of n-type Si layers doped with shallow donors produced by proton bombardment have been measured between 35 and 300°K. The donor ionization energy is (26 ± 1) meV. The donor concentration profile has been determined.

Frequency dependence of C and ΔV/Δ(C−2) of Schottky barriers containing deep impurities

Abstract The frequency dependence of ΔV/Δ(C −2 ) of Schottky barriers with deep impurities has been discussed on the basis of the depletion approximation. Systematic treatment has been developed of Schottky barriers having spatially distributed deep centers and useful expressions have been derived for ΔV/Δ(C −2 ) . It is shown that the impurity profile, the energy level and the electron emission rate of deep impurities can be determined by making measurements of the frequency dependence of ΔV/Δ(C −2 ) . The method of measuring ΔV/Δ(C −2 ) has also been briefly described.

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.

A NEW METHOD FOR DETERMINATION OF DEEP‐LEVEL IMPURITY CENTERS IN SEMICONDUCTORS

It is pointed out that the conventional capacitance method and the Copeland method provide different results for the determination of impurity concentrations of semiconductor wafers in the presence of deep centers. On the basis of a discussion of this phenomenon, a simple method of determining the concentration and the energy level of deep centers is proposed and demonstrated. The method is checked by application to oxygen‐doped n‐type GaAs with a carrier concentration of 3.2×1015 cm−3. The result yields a value of 2.1×1016 cm−3 for the deep center concentration and a value of 0.57 eV below conduction band for the energy level of the deep centers, which are reasonable in comparison with other experimental 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.

DLTS Study of RIE-Induced Deep Levels in Si Using p^+n Diode Arrays

Deep levels in Si induced by reactive ion etching (RIE) of SiO2 film have been studied by DLTS. In order to detect the RIE-induced damage existing near the surface region, special device structures consisting of p+n diode arrays are used. It is found that the dominant deep levels produced by RIE are four hole traps. One level at Ev+0.40 eV exhibits the Poole-Frenkel effect, from which it is identified as an acceptor. Another level at Ev+0.46 eV is deduced to be an interstitial iron level from the emission rate. There is a strong decrease in the deep level concentrations upon annealing above 500°C. However, the deep levels do not completely disappear upon annealing at high temperatures. The deep level concentrations correlate well with the current-voltage characteristics of the devices.

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.

Frequency Response of Gold Impurity Centers in the Depletion Layer of Reverse‐Biased Silicon p+n Junctions

The frequency dependence of ΔV/Δ(Crf−2), which is closely related to the space‐charge density of a reverse‐biased p+n junction containing deep impurities, is discussed by using Goodmans model. In order to measure the variation of ΔV/Δ(Crf−2) with frequency, a special technique has been developed. The experimental result on a gold‐doped silicon p+n junction shows that frequency dispersion of gold acceptors is well explained by assuming a single deep level, whose charging and discharging time constant is 8.0 × 10−4 sec at room temperature. A value of 1.25 × 103 sec−1 is obtained for the thermal emission rate of electrons from the gold acceptors, which agrees well with the data obtained from the photo and dark junction current and capacitance experiments. This result differs from that determined by capture rate measurements. The disagreement is removed by taking into account an electron capture process through the excited states of the gold acceptors under non‐equilibrium conditions.

Determination of the spatial distribution of deep centers from capacitance measurements of pn junctions

Effects of a spatial distribution of deep centers on the junction capacitance are reported for the first time. It is shown that the spatial distribution of deep centers can be calculated from capacitance data measured by both the capacitance‐voltage method and the Copeland method, if their energy level is known or assumed. The theory is examined with the experiment on silicon p+n junctions irradiated with 300‐kV protons. The analysis yields a value 0.40 eV below conduction band for the energy level of radiation‐induced defects, as well as a distribution of the defects with depth.