S.R.D. Kalingamudali

Perimeter and bulk recombination currents in GaAs homojunction diodes and heterojunction bipolar transistors after surface processing

Abstract The emitter-mesa surface (perimeter) and emitter-base bulk recombination currents, in GaAs AlGaAs heterojunction bipolar transistors (HBTs), are known to degrade device performance at low applied voltages, where these currents dominate. To study the effects of the etchant (used in defining the diode mesas) on the perimeter recombination current, GaAs homojunction diodes were given a short time etch in a selection of wet chemical etchants and the effect on the edge leakage current investigated. It was observed that the edge leakage current could be modified by the process used to fabricate the mesa. Following encouraging results, the work was extended to include GaAs AlGaAs HBTs, and an investigation was undertaken of the effects on recombination at the perimeter of the emitter-mesa and on bulk recombination current, with surface treatments. A simple model was used to separate the bulk and perimeter contributions from the recombination current. The surface recombination current was strongly dependent on the process used to define the mesa, and can therefore, by appropriate processing, be reduced.

Recombination current reduction in AlGaAs/GaAs heterojunction bipolar transistors with polyimide deposition

Abstract N-p-n AlGaAs/GaAs heterojunction bipolar transistors of various emitter-mesa diameters have been fabricated to examine the effects on the recombination current with polyimide deposition. The recombination current in these devices (when the ideality factor is close to 2) was proportional to the device perimeter before and after polyimide deposition. This suggests that the dominant component of the recombination current in these devices is the perimeter recombination current. A simple model was developed which allowed the contribution from the perimeter and bulk recombination currents to be calculated. The common-emitter d.c. current gains of these devices increased correspondingly as recombination current decreased due to the polyimide deposition.

Remote Controlling and Monitoring System to Control Electric Circuitry through SMS using a Microcontroller

Mobile phones have become one of the most popular communication devices among most of the people around the world, and short message service (SMS) is popular among mobile phone users as a cheap and convenient method of communicating. Therefore, SMS technology is a common feature with all mobile network service providers. Since the use of SMS technology is a cheap, convenient and flexible way of conveying data, researchers are trying to apply this technology in many different areas that were not provided by service providers at present. One of such areas that the SMS technology could be used as a cost effective and more flexible way will be remote monitoring and controlling. Therefore, a system has been developed to control and monitor electric circuitry through SMS using the PICmicroreg 16F877A microcontroller remotely. The microcontroller performs all the functions of the system. Standard attention commands are used to control the operation on SMS in the mobile phone. SMS is produced using the concept of protocol data unit

Current gain increase in AlGaAs/GaAs heterojunction bipolar transistors using AlGaAs layer overgrowth

Reduction of the surface recombination current components in Npn AlGaAs/GaAs heterojunction bipolar transistors has been achieved by overgrowing the emitter‐mesas with an AlGaAs layer approximately 0.5 μm thick. It was observed that the n=2 recombination current was reduced by ∼90%, to about 10% of the original value, with a corresponding 13‐fold increase in current gain for 270×20 μm2 devices. In addition, devices with the same emitter‐base area, but significantly different perimeters, were observed to have similar current gains and n=2 recombination current values. This was in contrast to devices fabricated without an overgrowth layer. These results suggest that the overgrowth layer causes a very significant reduction in the perimeter recombination current.

Pedestrian and vehicular traffic friendly uninterrupted solar powered traffic signal light system

During power failures and power cuts road users suffer immense difficulties due to non-availability of traffic signal lights all over the world. Use of solar cells with lead acid accumulators to provide required power and the use of light emitting diode (LED) displays to function as signal lamps to reduce the stored power consumption will be a feasible solution for the same. Since the LED display consists of a number of LEDs, visibility from side ways is better than the conventional signal lamp having a single light source. Failure of the lamp in the conventional signals halts the entire operation of the signal lamp but in the case of failures of few LEDs in a matrix will not cease the entire operation. In most of the LED display traffic light systems, set of LEDs will not illuminate even when only one of the LEDs burnt out since the set is connected in series. In this design, parallel sets of LEDs are connected in series, and therefore, only the defective LEDs will not be illuminated but all the others will be illuminated. Some major advantages of this system are uninterrupted operation around the clock throughout the year, very low maintenance cost for replacing LEDs and the lead acid batteries, and during the installation of new signal posts it is possible to erect the same as a wireless installation. Solar panel with an accumulator can provide power while infrared sensors and diodes could be used to transfer signals between each signal post, hence it is not necessary to dig across the road for control and power cables. For the safety and the convenience of the pedestrians and vehicular traffic, bi-color seven segment digital displays are available to indicate the waiting time and remaining moving time. Considering the signal light requirement for a country, the above solution will have a considerable impact on the national power grid

Simultaneous control of multiple line-loads each connected separately in series with a designed unit control using Radio Frequency and a mobile device

A unit which can be connected separately in series with each load to control multiple line-loads simultaneously using Radio Frequency (RF) and a mobile device has been developed during this study. Series connected remotely controllable regulators are not widely available commercially and the few available do not have the facility to control the multiple line loads using a mobile application along with a RF remote controller and also they are very expensive and even require an alternative wiring system. The designed regulator provides the convenience of controlling the current flow through appliances connected to a single line power supply. A triac is used to control the power supplied to the load, since it can control the current flow in both halves of an AC current. The gate terminal is triggered by using a diac. A Switch Mode Power Supply, powers the active components of the regulator using the voltage drop across the triac. The Bluetooth (HC-06) and RF (315 MHz RF receiver) modules are programmed to receive inputs from the user to switch ON/OFF or control the voltage supplied to appliances such as fans and light bulbs. The Graphical User Interface enables the user to control the appliances easily and much faster than in normal usage of mechanical switches. The timer which allows the user to define time intervals for predefined output levels, can set desired levels of outputs for the appliances. This feature is not currently available in normal regulators. The suggested method facilitate simultaneous use of RF and the mobile devices as well as the ability to control several appliances with a single unit enabling energy conservation and ease of use. The cost of designing the unit with discrete components being less than US

Design of an Inexpensive GPIB Interfaced Voltage Source

17, it can be concluded that the model is cost effective since this method suggests two modes of control of the appliances along with timer settings. [1-9].

Experimental evaluation of separate contributions to ideality factor for the base surface recombination current in heterojunction bipolar transistors

An inexpensive voltage source that can be controlled by a computer using the general purpose interface bus (GPIB) controller is designed since commercially available GPIB interfaced voltage sources are very expensive. The designed voltage source has been tested for regulation and compared with two commercial type power supplies. The power supply of the voltage source was constructed using the switch mode power supply (SMPS) method. Controlling the duty cycle of the pulse width modulator circuit the output voltage of the SMPS was regulated. PICmicroreg 16F877A microcontroller was used to control all operations of the GPIB interfaced voltage source

Remotely Controllable Regulator Connected in Series with Resistive and Inductive Loads

In this paper it is shown experimentally, for the first time, that the ideality factor n for the extrinsic base surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is unity and is bias independent. The devices with various emitter radii have been fabricated and the n = 1 and n = 2 current components of the emitter-base junction current were calculated. It was observed experimentally that the n = 1 current component was proportional to the total area of the emitter-base junction plus the exposed extrinsic base surface, both at lower biases such as emitter-base voltage V BE = 0.60 V (when the n = 2 current component dominates), and at higher biases such as V BE = 1.0 V (when the n = 1 current component dominates). The ideality factor value for the diffusion current is 1