T. P. Chen

Current transport and its effect on the determination of the Schottky-barrier height in a typical system: Gold on silicon

Abstract The measurements of photovoltage, internal photoemission, current-voltage (I-V) and capacitance-voltage (C-V) have been performed for Au on n-Si (111) within a temperature range of 7 to 300 K. The values of Schottky-barrier height at room temperature obtained from these four measurements are in very good agreement, but conflicting results have been obtained at low temperatures. The measurements of both the internal photoemission and the C-V show a negative temperature dependence of the barrier height which is almost identical to that of the indirect energy band gap in silicon, but the barrier height obtained from the photovoltage measurements and the I-V measurements strongly decreases as temperature decreases. In this paper, the influence of the current transport on the determination of the Schottky-barrier height is discussed, and it is demonstrated that the conflicting results may be explained well in terms of the recombination current involved in the photovoltage measurements and the I-V measurements.

The effect of the temperature dependence of the ideality factor on metal-semiconductor solar devices

The diode performance of Au/n-Si and Au/n-GaAs systems has been investigated within the temperature range of 100 K to 300 K. From the results of photovoltage and I-V measurements, the calculated solar cell efficiency of the Au/n-Si diode degrades significantly from the ideal case (n factor equal to 1). The change of the efficiency of the Au/n-GaAs system with temperature, however, adheres closely to the ideal case. The difference between the results of these two systems is explained by the recombination current effect, which appears to be more significant in the Au/n-Si system.

Interfacial Fermi level and surface band bending in Ni/semi-insulating GaAs contact

For nickel on the chemically clean surface of undoped semi‐insulating GaAs at room temperature, an upward surface band bending of 0.062 eV and a barrier height of 0.690 eV have been observed by the photovoltage and the internal photoemission techniques, respectively. The observed surface band bending is in excellent agreement with its predicted value, and the observed barrier height also agrees very well with its value from the very careful analysis of reversed I‐V data. It has been determined that the interfacial Fermi level lies at 0.690 eV below the GaAs conduction band minimum at the interface. The interfacial Fermi level is found to coincide with the energy level of the EL2 native defect, indicating the importance of the EL2 in the Fermi level pinning at the interface.

Theoretical study of leakage current effect on surface photovoltage induced by photoemission

Abstract Recent studies show that surface photovoltage (SPV) seriously affects the determination of the surface band bending by photoelectron spectroscopy. This work demonstrates that SPV is strongly affected by the leakage current which depends on the metal coverage and other experimental factors. The results of our calculation account for the observed reduction of SPV with increasing coverage and the strong photo-flux dependence of SPV. This study suggests the importance of the leakage current effect on SPV in the determination of the coverage-dependent surface band bending from photoemission experiments.

Reproducibility of transmission line measurement of bipolar I-V characteristics of MOSFETs

Reproducibility of transmission line (TL) measurement of bipolar current-voltage (I-V) characteristics of grounded gate MOSFETs has been examined. It is observed that the reproducibility is related to the duration of the pulses generated by the transmission line, and a longer pulse duration gives a better reproducibility. For a short pulse duration, it is more difficult to reproduce the I-V characteristics in the triggering region than in other regions (i.e., the pretriggering and snapback regions).

Reverse I-V characteristics of Au/semi-insulating InP (100)

The I-V characteristics of Au/semi-insulating InP (100) under reversed bias have been measured between 230 K and 290 K. A simple model based on the thermionic field emission theory (TFE) is proposed to describe this system. Based on this model, the value of the bandgap obtained from the I-V characteristics is in reasonable agreement with the literature. At room temperature, the corresponding fitted values of the barrier height Phi b and the series bulk resistance Rb are 0.68+or-0.05 V and 1.3207 Omega respectively.

A calculation of the photovoltage at the metal-semiconductor interface

Abstract The photovoltage at the metal-semiconductor interface has been calculated with a simple model in which the influence of thermionic emission, tunneling, carrier recombination and leakage has been considered. The dependence of the photovoltage on temperature, the Schottky barrier height, the lifetime of carriers and the leakage resistance is reported.

A study of recombination current in Schottky contacts by photovoltage measurements

Photovoltage measurements and internal photoemission measurements have been performed for Au/n-GaAs and Ag/n-GaAs contacts within the temperature range of 7 to 300 K. Reliable Schottky barrier heights (SBH) are determined from internal photoemission measurements which show that the SBH in both the contacts is independent of temperature, implying the interfacial Fermi level pinning relative to the conduction band minimum. It is found that the current transport processes such as thermionic emission, tunnelling and leakage current cannot be responsible for the observed photocurrent-photovoltage relationship for large photocurrent in the photovoltage measurements. The activation energies found for the current transport are actually the same in both the contacts, which are almost equal to half of the bandgap of GaAs, indicating that the recombination current is the dominant process. In addition, our results indicate that the equation currently used for the recombination current in Schottky contacts is generally over-simplified.

Determination of leakage resistance of Schottky contacts by photovoltage measurements

The leakage resistance of Schottky contacts has been determined from photovoltage measurements, thus allowing the contribution of the leakage current to the current transport in the Schottky contacts to be easily evaluated. It is found that under identical conditions of sample fabrication, different Schottky contacts have nearly the same leakage resistance. A comparison between a theoretical calculation and experimental data for the photocurrent‐photovoltage relationship shows that the leakage current becomes dominant at low temperatures and small photocurrents. In these regimes, the current transport is dominated by the leakage current, and as a result, a linear relation (the Ohmic rule) between the photocurrent and the photovoltage is observed.

Characterization of Pt‐Si interface by spectroscopic ellipsometry

Spectroscopic ellipsometric measurements for Pt/n‐Si samples with different thickness of Pt films have been performed. The thickness of the Pt films determined with the three‐phase model (air/Pt/Si) changes with the wavelength λ while that with the four‐phase model (air/Pt/interface layer/Si) remains unchanged, showing the existence of an interface layer. At the same time, the apparent optical dielectric constants of the interface layer as a function of λ are also obtained. A calculation based on the effective medium theory is carried out to simulate the optical dielectric data of the interface layer. Some structural information of the interface layer is obtained from the calculation.