M. Madheswaran

Numerical simulation of an ion-implanted GaAs OPFET

A numerical model of an ion-implanted GaAs optical field-effect transistor (OPFET) has been presented. The model is a physics-based one, and overcomes the major limitations of the existing models by considering both the photoconductive effect in the channel and photovoltaic effect at the gate Schottky barrier as well as the channel-substrate barrier. The exact potential profile in the channel and variation of gate depletion width and substrate depletion width in the channel as a function of position between source and drain have been computed for the first time for a nonuniformly doped channel. The model can be used to obtain the drain-current-drain-voltage characteristics, transfer characteristics, transconductance and gate-to-source capacitance of the device under dark and illuminated conditions. The model can be used as a basic tool for accurate simulation of optoelectronic integrated circuits (OEICs) using an OPFET.

Frequency dependent characteristics of an optically controlled InP MIS capacitor

Abstract The paper reports the results of theoretical studies on the effect of intensity modulated illumination on the characteristics of a novel MIS capacitor which utilizes InP:Fe as the semiconductor substrate and Al 2 O 3 as the insulator. The study reveals that the intensity modulated illumination causes significant changes in the characteristics of the device under illumination. The d.c. value of the capacitance depends on the peak value of the optical power while the fundamental component of the time varying capacitance of the device depends on the frequency of the signal modulating the intensity of the light. The semi-insulating nature of the semiconductor improves the photosensitivity of the device. A low value of the minority carrier lifetime enables the device to be used at higher frequencies compared to other MIS devices. The time varying capacitance of the device can be exploited for conversion of intensity modulated optical signal to frequency modulated electrical signal.

Numerical Simulation for Estimating the Optically Controlled Characteristics of an Ion-Implanted Si-MESFET

The paper presents a numerical model for determining the dc characteristic of an ion-implanted Si-MESFET under optically controlled condition. The model accounts for all the major effects that shape the characteristics of the device in the illuminated condition. For the first time a model has been developed for the optically controlled MESFET with non-uniformly doped channel to determine the channel voltage profile and the variation of the gate depletion width as well as the substrate depletion width in the channel as a function of position between source and drain. The model can also be utilised for estimating the drain current—drain voltage characteristics and the transfer characteristics of the device under dark and the illuminated condition. It also enables one to calculate the transconductance and the gate to source capacitance which are directly related to the cut-off frequency of the device.

Noise Analysis of InP/InGaAs Superlattice Avalanche Photodiode

A theoretical study of the noise characteristics of an InP/In0.53 Ga0.47 As Superlattice Avalanche photodiode (SL-APD) has been presented. It has been found that an improvement in the value of the effective hole-to-electron ionisation rate ratio (βeff/αeff) for the SL-APD structure results in a low-noise behaviour of the device. The device has a very high gain-bandwidth product (≈450 GHz) and a low excess noise factor at moderate gain. It is expected to find application as a highly sensitive low-noise photodetector in optical receiver unit for long-haul fiber optic communication system in 1.3 to 1.6 μm.

A proposed velocity-electric field relationship for modeling compound semiconductor devices

This paper proposes a new empirical relationship between the electron mobility and the applied electric field for compound semiconductors over the entire region including the negative differential mobility region. It ensures continuity and smoothness of v-E curve over the entire region which helps the convergence behavior in numerical simulation of compound semiconductor devices. The proposed approximation is in good agreement with reported experimental results and Monte-Carlo simulation results.

Large Signal Model of an Optically Controlled GaAs IMPATT Diode

A large signal model of an optically controlled Read-type GaAs IMP ATT diode has been presented. In contrast to other existing theories, we consider the effect of photogenerated carriers in the avalanche zone which significantly affects the device characteristics in the illuminated condition. The model presented here is used to examine the effect of illumination on the output power, efficiency and negative conductance of the device. It has been found that for constant bias current, the output power and efficiency of the device are strong functions of the incident optical power. The model can be used as a basic tool for optimising GaAs IMPATT diodes for optically controlled applications in microwave region.

Frequency response of time-varying photocapacitance of an InP:Fe MIS capacitor

In this paper the effect of intensity modulated illumination on the photocapacitance of an InP metal-insulator-semiconductor (MIS) structure has been reported. A theoretical model of the device has been developed and the results obtained on the basis of the model have been presented for determining the dependence of the time-varying photocapacitance of the device on the frequency of the signal modulating the intensity of incident illumination.