Optimization of the parameters of HEMT GaN/AlN/AlGaN heterostructures for microwave transistors using numerical simulation

The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.     

SiC and GaN transistors - is there one winner for microwave power applications?

Wide bandgap semiconductors show promise for high-power microwave electronic devices. Primarily due to low breakdown voltage, it has not been possible to design and fabricate solid-state transistors that can yield radio-frequency (RF) output power on the order of hundreds to thousands of watts. This has severely limited their use in power applications. Recent improvements in the growth of wide bandgap semiconductor materials, such as SiC and the GaN-based alloys, provide the opportunity to now design and fabricate microwave transistors that demonstrate performance previously available only from microwave tubes. The most promising electronic devices for fabrication in wide bandgap semiconductors for these applications are metal-semiconductor field-effect transistors (MESFETs) fabricated from the 4H-SiC polytype and heterojunction field-effect transistors (HFETs) fabricated using the AlGaN/GaN heterojunction. These devices can provide RF output power on the order of 5-6 W/mm and 10-12 W/mm of gate periphery, respectively. 4H-SiC MESFETs should produce useful performance at least through X band and AlGaN/GaN HFETs should produce useful performance well into the millimeter-wave region, and potentially as high as 100 GHz.     

Gallium nitride based high power heterojunction field effecttransistors: process development and present status at UCSB

The development of GaN based devices for microwave power electronics at the University of California, Santa Barbara (UCSB), is reviewed. From 1995 to 2000, the power performance of AlGaN/GaN-on-sapphire heterojunction field effect transistors improved from 1.1 W/mm to 6.6 W/mm, respectively. Compensating the disadvantages of the low thermal conductivity of the sapphire substrate through heat management via flip chip bonding onto AlN substrates, large periphery devices with an output power of 7.6 W were demonstrated. UCSB also fabricated the first GaN based amplifier integrated circuits. Critical issues involved in the growth of high quality AlGaN/GaN heterostructures by metal-organic chemical vapor deposition and the device fabrication are discussed     

Study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures

The results of numerical simulation and experimental study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures (p-HEMT) are considered. The possibility of correct simulation of static characteristics of actual device structures of p-HEMT transistors using the TCAD software package (SILVACO Inc.) is demonstrated. The essential necessity of using selective gate-groove etching to achieve controllable and reproducible device parameters is shown.     

Influence of annealed ohmic contact metals on electron mobility of strained AlGaN/GaN heterostructures

The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas (2DEG) is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors (AlGaN/GaN HFETs). Current-voltage (I-V) characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage (C-V) characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.     

基于AlGaN/GaN HEMT的功率放大器的研究进展

介绍了几类常见的基于AlGaN／GaN HEMT的微波功率放大器；论述了制造微波功率放大器的两种关键工艺技术——倒装芯片集成(FC-IC)和共平面线(CPW)；分析了自行研制的微波功率放大器核心器件AlGaN／GaN HEMT的性能。     

AlxGa1–xN—A New Material System for Biosensors

The applicability of the group III nitride material system for the fabrication of semiconductor‐based biosensors is demonstrated. The operation of ion‐sensitive field‐effect transistors (ISFETs) based on AlGaN/GaN heterostructures in aqueous electrolytes is shown to be characterized by high sensitivity and low drift. Fibroblasts in contact with oxidized and as‐deposited AlGaN surfaces are demonstrated to survive at least for 24 h, indicating that these surfaces are chemically robust and non‐toxic against living cells. Surface hydrophilization using thermal oxidation allows the deposition of highly mobile lipid membranes by vesicle fusion. The homogeneity and the diffusion properties of phospholipids with different net charges were analyzed by fluorescence microscopy and constant photobleaching, taking advantage of the optical transparency of the AlGaN material system. The obtained results reveal that AlGaN‐based devices are promising candidates for future multifunctional biosensors.     

Transverse spatial transport in field-effect transistors based on heterostructures with selective doping and the limits of applicability of quasi-hydrodynamic models

Semiconductors - For field-effect transistors based on heterostructures with selective doping, the results of calculations for the output characteristics of devices on the basis of the hydrodynamic...     

SAW Filters Composed of Interdigital Schottky and Ohmic Contacts on AlGaN/GaN Heterostructures

We proposed surface acoustic wave (SAW) filters composed of interdigital Schottky and ohmic contacts on AlGaN/GaN heterostructures. The contribution of the SAWs appeared in the radio frequency characteristics of the filters when the Schottky contacts were reverse biased. Onsets of the SAW signals and the threshold voltage of simultaneously fabricated high-electron mobility transistors were found to almost agree with one another. We also obtained an isolation of >40 dB. These results suggest that SAW-based functional devices are likely to be realized using AlGaN/GaN heterostructures with interdigital Schottky and ohmic contacts     

Thermal effects in AlGaN/GaN/Si high electron mobility transistors

Group III-nitride compounds are of increasing interest for designing high power and high temperature transistors. A considerable progress in the growth and process technology of these devices has been achieved. However, there are still limitations concerning particularly the lack of native substrates. Comparison of the AlGaN/GaN high electron mobility transistors investigated favours the SiC substrate. Recently, encouraging results have been reported for AlGaN/GaN/Si. The crucial problem found in AlGaN/GaN transistors operating at high biases is the self-heating induced by high power dissipation in the active zone. The present work reports on a study of the self-heating in AlGaN/GaN HEMTs grown on Si(1 1 1). The electron-band parameters of the heterostructures have been calculated self-consistently by taking into account the piezoelectric and spontaneous polarizations. As an experiment support, direct-current characteristics of AlGaN/GaN/Si HEMTs have been used to derive the drain voltage-dependent temperature rise in the conductive channel. As has been found, the self-heating is relatively weak. An improvement in the electron transport is achieved by optimizing the epilayers and adjusting the electrode sizes at output of the transistors investigated.     

The ALD Films of Al2O3, SiNx,and SiON as Passivation Coatings in AlGaN/GaN HEMT

Russian Microelectronics - In the field-effect transistors based on the wide-band-gap nitride heterostructures, the dielectric layers are in widespread use as one of the main elements in the active...     

effect of the parameters of AlN/GaN/AlGaN and AlN/GaN/InAlN heterostructures with a two-dimensional electron gas on their electrical properties and the characteristics of transistors on their basis

The effect of the layer thickness and composition in AlGaN/AlN/GaN and InAlN/AlN/GaN transistor heterostructures with a two-dimensional electron gas on their electrical and the static parameters of test transistors fabricated from such heterostructures are experimentally and theoretically studied. It is shown that the use of an InAlN barrier layer instead of AlGaN results in a more than twofold increase in the carrier concentration in the channel, which leads to a corresponding increase in the saturation current. In situ dielectric-coating deposition on the InAlN/AlN/GaN heterostructure surface during growth process allows an increase in the maximum saturation current and breakdown voltages while retaining high transconductance.     

Monolithically integrated high-power broad-band RF switch based on III-N insulated gate transistors

We report on the high-performance monolithically integrated RF switch based on metal-oxide-semiconductor III-N heterostructure field-effect transistors (MOSHFETs). The radio frequency (RF) switch microwave monolithic integrated circuit (MMIC) consists of three submicron-gate MOSHFETs connected into /spl pi/-type configuration. In the 0-10 GHz frequency range, the insertion loss is less than 1dB and the isolation is better than 20 dB. The switching powers well exceed 20 W per 1mm of the active element width. The high performance parameters of the switch are achieved due to unique properties of III-nitride MOSHFET, which combines a low channel resistance and high breakdown voltage features of AlGaN/GaN HFETs and extremely low gate leakage currents, large gate voltage swing and low gate capacitance specific to insulated gate design. The combination of these parameters makes MOSHFETs excellent candidates for high-power switching. The experimental data obtained from the RF switch are in close agreement with the results of simulations.     

Transient radiation effects in microwave monolithic integrated circuits based on heterostructure field-effect transistors: Experiment and model

The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 10¹² rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data.     

12 GHz $F_{rm MAX}$ GaN/AlN/AlGaN Nanowire MISFET

GaN/AlN/AlGaN/GaN nanowire metal–insulator–semiconductor field-effect transistors (MISFETs) have been fabricated for the first time with submicrometer gate lengths. Their microwave performances were investigated. An intrinsic current-gain cutoff frequency $(F_{T})$ of 5 GHz as well as an intrinsic maximum available gain $(F_{rm MAX})$ cutoff frequency of 12 GHz have been obtained for the first time and associated with a gate length of 0.5 $muhbox{m}$. These results show the great potentiality of GaN-based nanowire FETs for microwave applications.      

Imaging and Spectroscopic Sensing with Low-Repetition-Rate Terahertz Pulses and GaN TeraFET Detectors

Aiming for non-destructive testing and security applications, we investigate transmission-mode imaging and spectroscopic sensing using terahertz (THz) pulses from a commercial optical parametric oscillator (OPO) in combination with THz detectors based on antenna-coupled field-effect transistors (TeraFETs). The Q-switched OPO generates quasi-continuous-wave THz pulses with a peak power of up to 1 W at a repetition rate between 12 and 90 Hz. The pulses are frequency-tunable between 0.7 and 2.6 THz with a typical linewidth of 50 GHz. We explore detection with fast GaN/AlGaN TeraFETs which hold the potential for multi-pixel and homodyne detection.     

Electromagnetic Modeling,Technology, and Production of Microwave C<Superscript>3</Superscript>MOSHFET Switches on AlGaN/GaN Heterostructures

The features of the electromagnetic modeling of a microwave switch for the frequency range of 1–20 GHz, which is then produced by C³MOSHFET technology on AlGaN/GaN heterostructures using high-K dielectrics and contacts with capacitive coupling, are considered.     

Time-dependent degradation of AlGaN/GaN heterostructures grown on silicon carbide

The AlGaN/GaN heterostructure field-effect transistors (HFETs) were grown on 4H-SiC substrates by metal-organic chemical-vapor deposition (MOCVD) with a range of Al compositions (30–35%) and AlGaN barrier thicknesses. Films with higher strains exhibited a time-dependent degradation of the two-dimensional electron gas (2DEG) that varied from days to weeks. Atomic force microscopy (AFM) measurements of the degraded films revealed a hexagonal cracking pattern with an increase in the medium-scale surface roughness. The localized strain relaxation of AlGaN barriers and increased roughness of the AlGaN/GaN interface and AlGaN surface result in a broad shoulder at the lower angle of the AlGaN peak and a loss of satellite fringes in the (0006) reflection x-ray diffraction (XRD) curve. This degradation raises serious questions with regard to reliability and survivability of AlGaN HFETs and may complicate device fabrication.     

Low-frequency noise in AlGaN/GaN heterostructure field effecttransistors

We report low-frequency noise characteristics of doped-channel GaN/AlGaN heterostructure field-effect transistors grown on sapphire substrates. In the frequency range 1 Hz-100 kHz the observed noise is of the 1/f character. The Hooge constant is of the order of 10^-2 and is linearly proportional to the channel width. The noise originates in the fluctuation of carrier number in the channel due to relatively high density of defects at the GaN/AlGaN heterointerface     

11.2 W/mm power density AlGaN/GaN high electron-mobility transistors on a GaN substrate

In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f_max) and unity current gain cut-off frequency (f_t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.