C.Y. Chang

Optical and electrical current gain in an amorphous silicon bulk barrier phototransistor

An amorphous silicon (a-Si) bulk barrier phototransistor was successfully fabricated on a glass substrate. The measured optical gain G and electrical current gain HFEare 196 percent and 11.8, respectively. Estimation and measurement methods for G and HFEare discussed.

Spinodal decomposition and magnetic properties of Fe–Cr–12Co permanent magnet alloys

This report is concerned with the spinodal decomposition and magnetic properties of Fe–21∼30 Cr–12Co ternary alloys (by weight) as studied by transmission electron microscopy and magnetic measurements. Wavelength growth of the isothermally aged spinodal structure is found to be proportional to time1/3 for the later stage of aging at all aging temperatures, which suggests a coarsening process. Spinodal temperatures of these alloys are found to be higher than each of their Curie temperatures; nevertheless magnetic aging is effective in greatly improving the magnetic properties. Hence, a prerequisite of a higher Curie temperature in the magnetic aging theory is concluded to be unnecessary. Moreover, as the extrapolated onset spinodal wavelength, of 80–100 A, is superparamagnetic in nature, this suggests a prerequisite for the magnetic aging theory. Before magnetic aging can be operative, the particle should grow to a certain critical size, determined by the aging temperature and the anisotropy energy at that...

On the minority-carrier quasi-Fermi level in metal-oxide-semiconductor tunnel structures

Abstract This paper presents a theoretical study on the behaviors of the minority-carrier quasi-Fermi level (EFP) in the ultra thin (10–60 A) MOS tunnel structures under reverse bias. Considering the transport of carriers across the oxide layer and the electrostatic potential distribution in these diodes, the quantitative details of the energy difference between EFP and the metalFermi level (EFM), ΔE , at the semiconductor-oxide interface are reported and analyzed. Besides, the effects of ΔE on the electrical properties of MOS tunnel diodes are discussed. It is shown that ΔE is a measure of the driving force for the minority-carrier tunnel currents. For a given oxide thickness ( d ), ΔE , increases with the reverse bias ( VA ), approaching a saturation value when VA is greater than a critical voltage. This critical voltage refers to an electrical characteristics transition from the tunnel-limited mode to the semiconductor-limited mode, which increases with the oxide thickness. For a given bias, ΔE decreases with decreasing the oxide thickness. It is found that, for d ≤ 10 A , EFP is pinned to EFM; for d ≥ 60 A , EFP is pinned to EFN (the majority-carrier quasi-Fermi level in the semiconductor); for d ≤ 36 A and without external minority-carrier injection, the semiconductor surface can not reach strong inversion condition even when the reverse bias is sufficient high. For a given bias and oxide thickness, ΔE increases linearly with the logarithm of the external minority-carrier injection current. It is also shown that, for 20 ≤ d ≤ 50 A , the presence of interface states at the O-S interface causes a drastic reduction in ΔE ; while for other oxide thickness, the interface states have little influence on ΔE . The quantitative results presented in this article are of considerable importance in understanding the behaviors of the minority-carrier quasi-Fermi level in the MOS tunnel structures.

Enhancement of growth rate due to tin doping in GaAs epilayer grown by low pressure metal‐organic chemical vapor deposition

Tetraethyltin is used as an n‐type dopant in homoepitaxially growing GaAs films from triethylgallium and arsine vapor in a low pressure system. The experimental data show that the growth rate can be enhanced by tin doping. It is found that the deep level transient spectroscopy concentration of the electron trap located at about 0.8 eV below the conduction band is suppressed by Sn doping. Gallium vacancy may be attributed to the trap. A growth model has been proposed, which can be substantiated by the experimental results.

Amorphous silicon bipolar transistor with high gain (g12) and high speed (g30µs)

An n+/i/p /i/n+amorphous silicon bipolar transistor has been successfully fabricated with a current gain of 12 and a response speed of 30µS. This new structure of bipolar transistor has a very thin base (200A), therefore, high gain and high speed is obtainable. This device has a very promising applications as a flat panel display transistor and a phototransistor in photosensing element/array and photo coupler. Electrical and optical characteristics have been extensively investigated. Theoretical model and experimental results are plausibly in good agreement. Variation from the fundamental structure is also been developed such as the Schottky emitter Al/i/p+/i/n+bipolar transistor.

Photoreflectance study of the surface state density and distribution function of InAlAs

Photoreflectance is used to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface-intrinsic n+ structures having different undoped layer thicknesses. Experimental results indicate that, although the built-in electric field depends on the undoped layer thickness, there is a range of thickness within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we can determine that the surface states distribute over two separate regions within the energy band gap. The densities of the surface states are evaluated as well. Moreover, the dependence of the built-in electric field on undoped layer thickness is converted into the dependence of surface state density on the surface Fermi level in order to theoretically and exactly calculate the energy spectrum of the surface state density using a Guassian distribution function. The center and width of the distr...

Hot-carrier memory effect in an Al/SiN/SiO 2 /Si MNOS diode due to electrical stress

An Al/SiN(70 Å)/SiO2(126 Å)/(p)Si MNOS diode was fabricated by using the LOCOS process. The interface trap densities at SiN-SiO2and at the SiO2-Si interface were measured by a CV method. Successive stresses of biasing at -20 V introduces both trap densities. Memory effect of the flat-band shifts was observed. The electron traps were first produced at the SiN-SiO2interface. In addition, the hole traps were also produced owing to the two-step barrier formation in the insulators. Fowler-Nordheim tunneling may be responsible for the trapping in the oxide. The hole traps can be annealed while the electron traps cannot be.

Personal computer‐based automatic measurement system applicable to deep‐level transient spectroscopy

A simple, low‐cost, and flexible personal computer‐based automatic measurement system used for deep‐level transient spectroscopy (DLTS) is developed and implemented. An IEEE‐488 interface bus is designated for communication between the personal computer and instruments. This configuration provides advantages in ease of operation and quick set up, especially for the purpose of data acquisition and processing. In general, the system can be applied to any programmable measurement automatic configuration. A linear least‐square regression method is used to process the Arrhenius plot and to determine the activation energy. The DLTS signal and the Arrhenius plot are plotted and displayed during one thermal scan. A new DLTS computation algorithm has also been employed.

On occupation functions of donor- and acceptor-like interface states in metal-insulator-semiconductor tunnel structures

This paper presents a theoretical study on the occupation functions of interface states in MIS tunnel structures. Based on Shockley-Read-Hall (SRH) statistics and considering carriers tunneling between the metal and interface states, occupation functions of both donor- and acceptor-like interface states at arbitrary energy level within the semiconductor band gap are derived and analyzed. It reveals that, for the same energy level, the occupation functions of donor-like and acceptor-like interface states are remarkably different in magnitude. The deviation in occupation functions of these two types of interface states is a nonlinear function of the ratio of capture cross-section of the charge states to that of the neutral states (CC/CN) and the semiconductor surface conditions. If the insulating layer (SiO2) is relatively thick (> 50 A) or thin (< 10 A), interface states are in equilibrium with the semiconductor or the metal, respectively. Under the circumstances, the occupation functions of the two types of interface states are no longer distinguishable. Alternatively, they can be approximated by the well-known Fermi-Dirac distribution function. In this paper, quantitative influences of key parameters of MIS tunnel structures such as insulating layer thickness, electron and hole density at the semiconductor surface, capture cross-sections for charged and neutral states, etc., on interface states occupation function are discussed. For Gaussian-distributed donor- and acceptor-like interface states, the quantitative roles of interface states in charge storage and current-assisting effects are also demonstrated.

Two Dimensional Numerical Thermal Analysis of Silicon on Insulator Recrystallization Processes by a Moving Heat Source

The moving-zone melt recrystallization of polysilicon on insulator substrate has been studied with computer simulation methods. The most important parameters such as upper strip heater moving velocity, the power of upper strip heater, substrate temperature were investigated. Generally speaking, temperature profile in multilayer and melt depth of poly-Si are difficult to be visualized, but are still important for recrystallization process. Therefore by using two dimensional finite difference method, a numerical analysis of moving melt zone recrystallization processes has been developed. Through this analysis, the temperature profile in multilayer and melt depth of poly-Si are depicted.