Temperature Dependent Analytical Modeling, Simulation and Characterizations of HEMTs in Gallium Nitride Process

Research is being conducted for a high-performance building block for high frequency and high temperature applications that combine lower costs with improved performance and manufacturability. Researchers have focused their attention on new semiconductor materials for use in device technology to address system improvements. Of the contenders, silicon carbide (SiC), gallium nitride (GaN), and diamond are emerging as the front-runners. GaN-based electronic devices, AlGaN/GaN heterojunction field effect transistors (HFETs), are the leading candidates for achieving ultra-high frequency and high-power amplifiers. Recent advances in device and amplifier performance support this claim. GaN is comparable to the other prominent material options for high-performance devices. The dissertation presents the work on analytical modeling and simulation of GaN high power HEMT and MOS gate HEMT, model verification with test data and device characterization at elevated temperatures. The model takes into account the carrier mobility, the doping densities, the saturation velocity, and the thickness of different layers. Considering the GaN material processing limitations and feedback from the simulation results, an application specific AlGaN/GaN RF power HEMT structure has been proposed. The doping concentrations and the thickness of various layers are selected to provide adequate channel charge density for the proposed devices. A good agreement between the analytical model, and the experimental data is demonstrated. The proposed temperature model can operate at higher voltages and shows stable operation of the devices at higher temperatures. The investigated temperature range is from 1000K to 6000K. The temperature models include the effect of temperature variation on the threshold voltage, carrier mobility, bandgap and saturation velocity. The calculated values of the critical parameters suggest that the proposed device can operate in the GHz range for temperature up to 6000K, which indicates that the device could survive in extreme environments. The models developed in this research will not only help the wide bandgap device researchers in the device behavioral study but will also provide valuable information for circuit designers

The physics and technology of the InAlAs/n⁺-InP heterostructure field-effect transistor

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (p. 135-140).by David Ross Greenberg.Ph.D

Dual material gate field effect transistor (DMG-FET)

Improving performance and suppressing short channel effects are two of the most important issues in present field effect transistors development. Hence, high performance and long channel like behaviors are essential requirements for short channel FETs. This dissertation focuses on new ways to achieve these significant goals. A new field effect transistor - dual material gate FET (DMG-FET) - is presented for the first time. The unique feature of the DMG-FET is its gate which consists of two laterally contacting gate materials with different work functions. This novel gate structure takes advantage of material work function difference in such a way that charge carriers are accelerated more rapidly in the channel and the channel potential near the source is screened from the drain bias after saturation. Using HFET as a vehicle, it is shown that the drive current and transconductance in DMG-FET are therefore substantially enhanced as compared to conventional FET. Moreover, it is observed that the short channel effects such as channel length modulation, DIBL and hot-carrier effect are significantly suppressed. Numerical simulations are employed to investigate the new device structure and related phenomenon. A simple and practical DMG-HFET fabrication process has been developed. The proposed DMG-HFET is thus realized for the first time. Experimental results exhibit improved characteristics as the simulation results predicted

Direct optical control of a microwave phase shifter using GaAs fieldeffect transistors

The design and analysis of a novel optical-to-microwave transducer based upon direct optical control of microwave gallium arsenide (GaAs) field-effect transistor (FET) switches is the subject of this thesis. The switch is activated by illuminating the gate depletion region of the FET device with laser light having a photon energy and wavelength appropriate to the generation of free carriers (electron-hole pairs) within GaAs. The effects of light on the DC and microwave properties of the GaAs FET are explored and analyzed to permit the characterization of the switching performance and transient response of a reflective microwave switch. The switch is novel in that it utilizes direct optical control, whereby the optically controlled GaAs FET is directly in the path of the microwave signal and therefore relies on optically-induced variations in the microwave characteristics of the switch. This contrasts with previous forms of optically controlled switches which rely on indirect methods with the optical stimulus inducing variations in the DC characteristics of the GaAs FET, such that there is no direct interaction between the optically illuminated GaAs FET and the microwave signal. Measured and simulated results relating to the switching performance and transient response of the direct optically controlled microwave switch have been obtained and published as a result of this work. For the first time, good agreement is achieved between the measured and simulated results for the rise and fall times associated with the transient response of the gate photovoltaic effect in optically controlled GaAs FET switches. This confirms that the GaAs FET, when used as an optically controlled microwave switch, has a transient response of the order of several micro-seconds. An enhanced model of the GaAs FET switch has been developed, which represents a more versatile approach and leads to improved accuracy in predicting switching performance. This approach has been shown to be valid for both optical and electrical control of the GaAs FET. This approach can be used to model GaAs FET switches in discrete or packaged forms and predicts accurately the occurrence of resonances which may degrade the switch performance in both switching states. A novel method for tuning these resonances out of the switch operating band has been developed and published. This allows the switch to be configured to operate over the frequency range 1 to 20 GRz. The agreement between the models and measured data has been shown to hold for two very different GaAs FET structures. The results of the direct optically controlled microwave GaAs FET switch have been used as the basis for the design of a novel direct optically controlled microwave phase shifter circuit; Measured and simulated results are in good agreement and verify that the performance of the optically controlled phase shifter is comparable with previously published results for electrically controlled versions of the phase shifter. The 10 GRz phase shifter was optically controlled over a 1 GRz frequency range and exhibited a mid-band insertion loss of 0.15 dB. The outcome of the work provides the basis for directly controlling the phase of a microwave signal using the output of an optical sensor, with the GaAs FET acting as an optical-to-microwave transducer through a monolithic interface

The Third International Symposium on Space Terahertz Technology: Symposium proceedings

Papers from the symposium are presented that are relevant to the generation, detection, and use of the terahertz spectral region for space astronomy and remote sensing of the Earth's upper atmosphere. The program included thirteen sessions covering a wide variety of topics including solid-state oscillators, power-combining techniques, mixers, harmonic multipliers, antennas and antenna arrays, submillimeter receivers, and measurement techniques

A physics-based analytical model of an AlGaN/GaN high electron mobility transistor

Popular semiconductors currently being used for RF applications include GaAs and InP. The operating frequencies for HEMTs built with these semiconductors covers the range from 800 MHz to 100 GHz. Although high-speed operation is attainable using GaAs or InP, product performance is limited when considering high-power applications, where a high breakdown field and thermal conductivity is needed. Proposed about fifteen years ago as a solution to this problem, GaN has emerged as a viable candidate to challenge, and perhaps overtake, GaAs and InP as the dominant semiconductor in RF products, particularly power amplifiers. This is due to its high breakdown field, large band gap, and high thermal conductivity (relative to InP and GaAs). GaN possesses other material parameter values that are favorable to existing technologies such as carrier saturation velocity, dielectric constant, and piezoelectric coefficients. On a worldwide scale, researchers and industry experts continue to work on the modeling of GaN-based HEMT devices in hope that GaN can be used commercially in the near future. The proposed model is physics-based, making use of the Schrodinger and Poisson equations to establish relationships between the sheet carrier density, Fermi Level, and device terminal voltages. The quantum well formed at the heterointerface is approximated as a triangular well with two eigenstates, both determined from the Schrodinger equation. The charge control equations were carried over into the I/V derivations and channel charge derivations for capacitance calculations. Spontaneous and piezoelectric polarizations at the heterointerface are responsible for the high density of carriers in the channel and are accounted for in the model in the expression for the device threshold voltage. Device performance is dictated by the aluminum mole fraction of the barrier layer. This is because the mole fraction controls the amount of polarization at the heterointerface and consequently the 2DEG density. I/V equations were derived incorporating both drift and diffusion components. A two region model was adopted for the saturation region to account for channel length modulation. Device conductances were derived from the drain current expressions and results compared to experimental data gathered. To address high frequency device behavior, parasitic gate capacitance (Cgs and Cgd) expressions and cutoff frequency expressions are derived and presented. High voltage conditions were assumed for the drain bias to simulate a high power scenario. Relationships between the cutoff frequency of the device, the length of the gate, and drain bias are shown and compared with published data reported by other authors

Cryogenic Ultra-Low Noise InP High Electron Mobility Transistors

Indium phosphide high electron mobility transistors (InP HEMTs), are today the best transistors for cryogenic low noise amplifiers at microwave frequencies. Record noise temperatures below 2 K using InP HEMT equipped cryogenic low noise amplifiers (LNAs) were demonstrated already a decade ago. Since then, reported progress in further reducing noise has been slow. This thesis presents new technology optimization, modeling, measurements and circuit implementation for the cryogenic InP HEMT. The findings have been used to demonstrate a new record minimum noise temperature of 1 K at 6 GHz. The thesis considers aspects all the way from material, process and device design, to hybrid and monolithic microwave integrated circuit (MMIC) LNAs. The epitaxial structure has been developed for lower access resistance and improved transport characteristics. By investigating device passivation, metallization, gate recess etch, and circuit integration, low-noise InP HEMT performance was optimized for cryogenic operation. When integrating the InP HEMT in a 4-8 GHz 3-stage hybrid LNA, a noise temperature of 1.2 K was measured at 5.2 GHz and 10 K operating temperature. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz. The low-frequency 1/f noise in the 1 Hz to 1 GHz range and gain fluctuations in the 1Hz to 100 kHz range have been measured for six different types of HEMTs, and compared to two different SiGe heterojunction bipolar transistors (HBTs). The results showed that radiometer chop rates in the kHz range are needed for millimeter wave radiometers with 10 GHz bandwidth. A comparative study of GaAs metamorphic HEMTs (mHEMTs) and InP HEMTs has been performed. When integrated in a 4-8 GHz 3-stage LNA, the InP HEMT LNA exhibited 1.6 K noise temperature whereas the GaAs mHEMT LNA showed 5 K. The observed superior cryogenic noise performance of the InP HEMT compared to the GaAs MHEMT was related to a difference in quality of pinch-off as observed in I-V characteristics at 300 K and 10 K. To demonstrate the low noise performance of the InP HEMT technology, a 0.5-13 GHz and a 24-40 GHz cryogenic monolithic microwave integrated circuit (MMIC) LNA was fabricated. Both designs showed state-of-the-art low noise performance, promising for future radio astronomy receivers such as the square kilometer array