R. U. Khan

Optically-controlled ion-implanted GaAs MESFET characteristic with opaque gate

An analytical modelling has been carried out for an ion-implanted GaAs MESFET having a Schottky gate opaque to incident radiation. The radiation is absorbed in the device through the spacings of source, gate, and drain unlike the other model where gate is transparent/semitransparent. Continuity equations have been solved for the excess carriers generated in the neutral active region, the extended gate depletion region and the depletion region of active (n) and substrate (p) junction. The photovoltage across the channel and the p-layer junction and that across the Schottky junction due to generation in the arc region of the gate depletion layer are the two important controlling parameters. The I-V characteristics and the transconductance of the device have been evaluated and discussed.

Analysis of GaAs OPFET with improved optical absorption under back illumination

The effect of back illumination with improved optical absorption has been analyzed for an ion-implanted GaAs OPFET considering the Pearson IV distribution of impurities. Plots have been made for two photo voltages developed across the substrate active layer junction and the Schottky junction. The drain-source current is significantly enhanced for the device when a fiber is inserted up to the active layer substrate junction compared with the case where the finite substrate effect is taken into account.

Frequency-dependent characteristics of an ion-implanted GaAs MESFET with opaque gate under illumination

Commercial metal-semiconductor-field-effect transistors (MESFETs) have opaque gate. We present here the frequency-dependent characteristics of an ion-implanted GaAs MESFET with opaque gate under illumination. The incident light enters the device through the gate-source and gate-drain spacings. Two photovoltages are developed: one across the Schottky junction due to generation in the side walls of the depletion layer below the gate and the other across the channel-substrate junction due to generation in the channel-substrate depletion region. The frequency dependence of the two photovoltages along with channel charge, drain-source current, transconductance and channel conductance of the device have been studied analytically and compared with the published theoretical results. For the first time, a commercially available GaAs optically illuminated field-effect transistor (OPFET) has been analyzed for frequency dependent characteristics instead of the transparent/semitransparent gate OPFET.

Optical effect in InAlAs/InGaAs/InP MODFET

Analytical results have been presented for an optically illuminated InAlAs/InGaAs/InP MODFET with an opaque gate. Partial depletion of the active region is considered. The excess carriers due to photo generation are obtained by solving the continuity equation. The energy levels are modified due to the generation of carriers. The surface recombination effect has also been taken into account. The results of I-V characteristics have been compared under dark conditions, since under illumination experimental results are not available. The offset voltage, sheet concentration, I-V, and transconductance have been presented and the effect of illumination discussed.

Time dependent analysis of an ion-implanted GaAs OPFET

A time-dependent analysis of the electrical characteristics of an ion implanted GaAs optical field effect transistor (OPFET) has been carried out. Both the cases of light turning on and off at a reference time t=0 have been considered. The photovoltaic effect across the Schottky junction and the depletion width modulation in the active layer have been taken into account. The threshold voltage, channel charge, channel conductance, drain-source current, transconductance, and gate-source capacitance of the device under light turning on and off conditions have been evaluated. When light is turned on, all the parameters increase with time before reaching the steady-state value and when light is turned off, these parameters decrease with time and reach their respective values corresponding to dark condition. The time under on condition is less than that under off condition. >

MITATT mode in DDR heterostructure Impatt

Large signal characterisation of double heterostructure DDR Impatt diode has been carried out in the millimeter-wave range considering the MITATT mode of operation. The structure of the device is p+-p2-p1-n1-n2-n+ where impact ionisation and tunneling takes place in the p1-n1 region. In this study we have considered two well-known heterostructures, e.g., InP/GaInAs/InP and InP/InGaAsP/InP and one nonconventional structure GaAs/InP/GaAs. The theoretical results of the performances of these devices as regards of output power, efficiency, and negative conductance revealed that the structures are quite promising as the source of power in the millimeter-wave range. The analysis may be used for other mm wave DDR heterostructure Impatts.

Light dependence of SOI MOSFET with nonuniform doping profile

The light dependence of a fully depleted short channel silicon-on-insulator (SOI) MOSFET is investigated. As the photon flux density increases, there is a lowering in the surface potential barrier called the photon induced barrier lowering (PIBL). The threshold voltage shows a logarithmic reduction with the increase in the incident flux density. The drain source current and the transconductance significantly increase under the incident optical flux density. The device will be useful for high speed application in optical systems.

Frequency dependent behaviour of an ion implanted GaAs OPFET considering the photovoltaic effect and the gate depletion width modulation

Abstract The frequency dependent behaviour of an ion implanted GaAs OPFET has been presented, considering the photovoltaic effect due to signal modulated incident radiation on the transparent/semitransparent Schottky gate of the device and the gate depletion width modulation. The results show that the signal frequency has significant effect on the device parameters between 107 and 1012 Hz. Below 107 Hz and above 1012 Hz the device parameters become independent of the signal frequency because the a.c. terms are negligible compared to their d.c. counterparts. The photovoltage, drain-source current and channel conductance have been plotted and discussed. The device works in the enhancement mode.

Generalized dc model of GaAs optical field effect transistor considering ion-implanted profile

Basic concepts and theory are developed for the effect of optical radiation on the dc characteristics of a generalized model of an ion-implanted GaAs metal-semiconductor field effect transistor (MESFET). The optical radiation is allowed to fall on a transparent or semitransparent Schottky gate and the spacing between the gate source and gate drain. The continuity equations are solved for the excess carriers in the depletion region below the Schottky gate in the channel region and in the depletion region at the junction of the active layer and the substrate. The current-voltage (/- V) characteristics show a remarkable enhancement in the drain source current compared to opaque gate optically controlled field effect transistor (OPFET) (a special case of the generalized dc model). This highlights the importance of two photovoltages developed across the Schottky junction and the channel-substrate junction. The transconductance, the channel conductance, and the photovoltages are also observed to be strongly affected by the flux densities.

Effect of Impurity Concentration and Biasing-Current Density on the Performance of a New DDR Heterojunction Impatt Diode

Large-signal analysis has been carried out for a new DDR Heterojunction Impatt diode to study the effect of biasing-current density and impurity concentration of the power and efficiency of the device. The structure of the device is P+—P2—P1—n1—n2—n+reverse biased to avalanche breakdown. P1—n1regions give the avalanche zone and P2 and n2 regions, the drift zones. Three structures have been considered, namely GaAs—Ge—GaAs, GaAs—Ge—Ge and Ge—Ge—GaAs. The first structure has two heterojunctions (i.e. P2—P1 and n1—n2 and second and third have one heterojunction (P1—P2 in second and n1—n2 in third). P1—n1, junction is of Ge in all the three structures.Plots of power and efficiency for these structures as a function of biasing-current density and impurity concentration reveal that in general, DDR H.J. Impatt diodes give more power and efficiency than the conventional GaAs DDR Impatts. GaAs/Ge/GaAs combination is found to be the best structure both in power and efficiency. The increase in efficiency is of the or...