Muhammad Navid Anjum Aadit

High Electron Mobility Transistors: Performance Analysis, Research Trend and Applications

In recent years, high electron mobility transistors (HEMTs) have received extensive atten‐ tion for their superior electron transport ensuring high speed and high power applica‐ tions. HEMT devices are competing with and replacing traditional field‐effect transistors (FETs) with excellent performance at high frequency, improved power density and satis‐ factory efficiency. This chapter provides readers with an overview of the performance of some popular and mostly used HEMT devices. The chapter proceeds with different struc‐ tures of HEMT followed by working principle with graphical illustrations. Device perfor‐ mance is discussed based on existing literature including both analytical and numerical models. Furthermore, some notable latest research works on HEMT devices have been brought into attention followed by prediction of future trends. Comprehensive knowl‐ edge of up‐to‐date results, future directions, and their analysis methodology would be helpful in designing novel HEMT devices.

Stark effect on InP-InGaAs separate absorption and multiplication avalanche photodiodes

We present electro-optical effects on Separate Absorption and Multiplication (SAM) Avalanche Photodiodes (APDs) with the presence of an external electric field. This effect is the well-known Stark Effect. We present optical shifts of SAM APDs with electric field variation and find that photons with lower energy can be absorbed to generate high photocurrent if Stark Effect is present. We demonstrate the change in absorption coefficient and exciton peak behavior with Stark Effect. We also present Stark Effect on photocurrent of SAM APDs by showing variation of responsivity. We use an in-house built Poisson-Schrödinger solver to simulate InP-InGaAs SAM APDs, as example. Thus, in this paper, we introduce a novel way to control and improve photocurrent of SAM APDs that can be extended to other APDs and used in optical modulators.

Dependence of threshold voltage on doped layer thickness in AlGaN/GaN HEMT: An improved split donor E-mode design

We present a novel and simple technique to control the threshold voltage of AlGaN/GaN High Electron Mobility Transistors. We use an in-house built self-consistent Schrödinger-Poisson simulator to model the dependence of threshold voltage of HEMT on its doped layer thickness. The simulator has been designed for finding the optimum threshold voltage for required mode of operation by changing doped layer thickness. It is shown that we can achieve enhancement mode of operation by reducing the doped layer thickness. However, this technique has a tradeoff that it reduces current too. Finally, an improved split donor enhancement mode HEMT design is proposed that effectively reduces doped layer thickness without minimizing current. The proposition would be helpful in designing enhancement mode devices at low cost.

Estimation of polarization charge in nitride based MODFETs using differential threshold voltage technique

We propose a novel method to estimate net polarization charge of nitride-based Modulation-doped Field Effect Transistors (MODFETs) introducing the concept of differential threshold voltage. We simulate MODFET device using an in-house built self-consistent Poisson-Schrodinger solver and calculate net polarization charge present in the device that can be efficiently used for improving device performance. Polarization increases electron charge density and consequently improves device speed and current. In this paper, we show the simulated results of AlGaN/GaN MODFET as an example and verify the accuracy of our charge calculation procedure by comparing our results with related works. Accurate knowledge of net polarization charge using the proposed estimation technique would provide better control of device characteristics.

Suppression of white and colored noise in Bangla speech using Kalman filter

We introduce adaptive Kalman filter approach for suppression of white and colored noise that corrupts Bangla speech. It is difficult to retrieve the desired information from noise corrupted speech signals. Bangla speech is frequently corrupted by white and colored noise in chaotic environment and so noise suppression is extremely necessary for smooth communication purpose. Background noise in Bangla speech may be stationary or dynamic in nature. Kalman filter is a well-known recursive filter that enhances speech signals corrupted by both static and dynamic noises. In this paper, we apply adaptive Kalman filter and show that it effectively reduces white and colored noise from corrupted Bangla speech and retrieves the information carried by the original speech. We compare the retrieved speech to the corresponding noise-free speech in terms of pitch values and analyze error to evaluate performance of the proposed filter. We take oral speech as voice record by native Bangla speakers and work with both vowels and consonants to show the feasibility of Kalman filter in both cases. Both male and female voices are analyzed to prove the effectiveness of the filter for Bangla speech irrespective of gender. Elimination of noise would provide non-disruptive communication in Bangla enhancing the efficacy of Bangla speech processing.

Pitch and formant estimation of bangla speech signal using autocorrelation, cepstrum and LPC algorithm

In this paper, we present comparative study of digital speech processing on Bangla speech signal. We represent oral characteristics of Bangla alphabet in terms of pitch and formant. We worked with both vowels and consonants to show their difference in practical use. We take oral speech signals as voice record and extract phonemes to analyze in both time and frequency domains. Both male and female voices are included in the analysis to find the effect of gender on Bangla voice speech. We verify our work by showing similarity of the results in time and frequency domains. We calculate first three formants of Bangla phonemes to show their relative impacts on Bangla speech. This extensive study of Bangla speech would provide listed information and data for further research to extract some other important features in this field.