T. Tauqeer

Two-Dimensional Physical and Numerical Modelling of InP-based Heterojunction Bipolar Transistors

State-of-the-art HBTs were designed, grown, fabricated and characterized in-house. The novelty of this process was the use of dimeric phosphorus generated from a Gallium Phosphide (GaP) decomposition source, which permitted growth at a fairly low temperature (420degC) while conserving extremely high quality materials. A self-aligned transistor with an emitter area of 5times5 mum2 demonstrated a low offset voltage of 150 mV and high current gain of 90. An excellent agreement with the measured data was achieved using physical modelling packages developed by SILVACO.

Elimination of Current Blocking in Ternary InAlAs-InGaAs-InAlAs Double Heterojunction Bipolar Transistors

Molecular beam epitaxy-grown wafers are used to fabricate all ternary In_0.52Al_0.48As-In_0.53Ga_0.47As-In_0.52Al_0.48As double heterojunction bipolar transistors (DHBTs) with knee voltages of less than 1 V, showing no current blocking characteristic even at current densities of 200 kA/cm². A set of wafers with a judicious combination of doping interface dipoles and composite collector designs were grown, and devices with a wide range of emitter areas from 20 × 20 down to 1 × 5 μm² were fabricated to investigate the effects of the different epitaxial and geometrical design tradeoffs that culminated in an optimum design that is able to achieve high breakdown and high current gain without introducing current blocking. Despite the use of a heavy dipole doping of 4 × 10¹⁸ cm^-3, a breakdown voltage BV_CEO of 5.8 V at 0.2 kA/cm² is achieved at room temperature. We believe this to be the first demonstration of an all-ternary large band gap InAlAs-InGaAs-InAlAs DHBTs with no current blocking up to a high current density of 200 kA/cm². These new DHBTs that use only ternary alloys may lead to simplified device growth and fabrication options and give deeper understanding of the design tradeoffs in these structures.

Detailed Analysis on the Spectral Response of InP/InGaAs HPTs for Optoelectronic Applications

We analyze an analytical spectral-response model for heterojunction phototransistors (HPTs) in order to understand the behavior of lattice-matched InPZIn0.47Ga0.53As HPTs with changing device and material parameters. The preliminary modeling of the spectral response lead to a good agreement between theoretical and experimental results for incident wavelength radiations at 980, 1310, and 1550 nm. We then performed several simulations in order to determine the individual influences of several parameters, such as the base-layer thickness and the surface-recombination velocity on the responsivity of the device. A decreasing trend for the surface-recombination parameter with increasing wavelengths was observed, and it is attributed to the greater recombination rate for high-energy photons generated near the surface.

Energy extraction from RF/ Microwave signal

The objective of this work is to use the concept of energy harvesting i.e. to receive Radio Frequency (RF) and Microwave signals present in the atmosphere and converting these signals into DC, in order to store it or power some circuit like charging a mobile. To implement this concept, an antenna is required to capture RF and microwave frequencies of GSM and WiFi signals in the surrounding. Designing an antenna is the focal point in realization of wireless cellular charging device. RF signals cannot be used to drive a load such as battery of a mobile phone, therefore rectification and a boost up is required done in the third phase which is Voltage Boosting and Rectification. A complete implemented system is being proposed in this paper with successful demonstration of using GSM-900 and GSM-1800 signals for charging a cellular phone. The research paper is a contribution towards the concept of wireless energy transmission at the same time it proves the idea of collecting and converting GSM and WiFi signals, to drive our low power consuming devices, from Radio towers and other wireless transceivers that is of no use otherwise.

Physical Modelling of a Step-Graded AlGaAs/GaAs Gunn Diode and Investigation of Hot Electron Injector Performance

This paper presents continuing work on the development of a novel physical model for an advanced GaAs Gunn diode with hot-electron injection. The device itself is commercially manufactured by e2v Technologies (UK) Ltd. for use in 77 GHz automotive Adaptive Cruise Control (ACC) systems. A 2D model has been developed using SILVA CO. Simulated IV characteristics are presented and shown to match well with measured data over a range of temperatures. The relationship between doping spike carrier concentration in the injector and asymmetry in the devices IV characteristic is then examined and compared to measured data.

GHz Class Low-Power Flash ADC for Broadband Communications

A low-power (~400 mW) high-speed (2-4 GS/s) 4-bit analogue-to-digital converter (ADC) based on InP/InGaAs heterojunction bipolar transistors (HBT) has been designed and simulated. The technology utilised two novel developments. Firstly stoichiometric conditions permitted growth at a relatively low temperature (420degC) while conserving extremely high-quality materials. Secondly dimeric phosphorus generated from a gallium phosphide (GaP) decomposition source has lead to excellent device properties. The complete ADC shows state-of-the-art performance and includes an interface for connection to standard digital signal processing (DSP) systems whilst dissipating only 400 mW.

Compact dual band microstrip antenna design using slits

This Paper presents the design and implementation of a microstrip patch antenna working for concurrent devices. Those devices are particularly targeted in this work whose operating frequency is 2.7GHz and 4.5GHz. Slits on the structure are placed to lengthen the current path on the surface which results in size reduction. The designed patch has compact size (16×14×1.6 mm3) that makes it beneficial for the size constrained electronic devices. To enhance the gain of the antenna, single patch was extended in the form of an array using corporate feed. The gain thus, increased from -4.32dBi to 3.05dBi. Simulations of the presented antenna are carried out using High Frequency Structure Simulator (HFSS) and it is fabricated on FR-4 substrate. Antenna is tested using Vector Network Analyzer (VNA).

Temperature studies of InAlAs-InGaAs-InAlAs double heterojunction bipolar transistors with no current blocking

In this paper, elimination of current blocking for the temperature range 77 K to 400 K is experimentally demonstrated for all ternary InAlAs–InGaAs–InAlAs double heterojunction bipolar transistors of emitter area 100 × 100 µm2. The wafers were grown by molecular beam epitaxy without using any complex growth techniques such as coherent heterointerfaces for reflection and penetration superlattice or quaternary alloys for grading. A room temperature breakdown (BVceo) of 5 V is achieved despite the collector thickness of less than 2000 A and heavy dipole doping of 4 × 1018 cm−3. Activation energies calculated from the Gummel plots indicate the shift of the transport mechanism across the junction from thermionic emission to predominantly tunneling as the temperature is lowered to 77 K.

A triple-band antenna array for next-generation wireless and satellite-based applications

In this paper, a triple-band 1 × 2 and 1 × 4 microstrip patch antenna array for next-generation wireless and satellite-based applications are presented. The targeted frequency bands are 3.6, 5.2 and 6.7 GHz, respectively. Simple design procedures and optimization techniques are discussed to achieve better antenna performance. The antenna is designed and simulated using Agilent ADS Momentum using FR4 substrate (e r = 4.2 and h = 1.66 mm). The main patch of the antenna is designed for 3.6 GHz operation. A hybrid feed technique is used for antenna arrays with quarter-wave transformer-based network to match the impedance from the feed-point to the antenna to 50 Ω. The antenna is optimized to resonate at triple-bands by using two symmetrical slits. The single-element triple-band antenna is fabricated and characterized, and a comparison between the simulated and measured antenna is presented. The achieved simulated impedance bandwidths/gains for the 1 × 2 array are 1.67%/7.75, 1.06%/7.7, and 1.65%/9.4 dBi and for 1 × 4 array are 1.67%/10.2, 1.45%/8.2, and 1.05%/10 dBi for 3.6, 5.2, and 6.7 GHz bands, respectively, which are very practical. These antenna arrays can also be used for advanced antenna beam-steering systems.

Signal analysis, design methodolgy, and modular development of a TR module for phased array radars

Phased array radars have received considerable importance both in commercial and defense communications. Lot of research has been carried out regarding development of its necessary components such as the antenna array, transmit/receive module (TRM) and processor unit. The cost, efficiency, wide bandwidth, and fabrication technology for the TRM have been pursued as key research areas. Cost reduction techniques till date have focused on the use of high tech MMIC fabrication techniques. Literature lacks in guiding a novice design engineer working on TRM in a cost effective manner. This paper presents mathematical analysis of signals processed in a TRM to enable a design engineer understand the constraints involved in the system design. The behavioral simulation, at 2.0 GHz, of TR module has been performed and, simulated results of phase shifter and TR switch sub-modules are also presented. Detailed system simulation is performed using lumped components for cost effective implementation in a lab environment. The results depict a close realization of the mathematical formulation.