This timely second edition has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements. Acknowledging that GaN transistors are not one-to-one replacements for the current MOSFET technology, this book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and applications. Included are discussions on the fundamental physics of these power semiconductors, layout and other circuit design considerations, as well as specific application examples demonstrating design techniques when employing GaN devices.

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GaN Transistors for Efficient Power Conversion

There is renewed emphasis on development of robust solid-state sensors capable of uncooled operation in harsh environments. The sensors should be capable of detecting chemical, gas, biological or radiation releases as well as sending signals to central monitoring locations. We discuss the advances in use of GaN-based solid-state sensors for these applications. AlGaN/GaN high electron mobility transistors (HEMTs) show a strong dependence of source/drain current on the piezoelectric polarization-induced two-dimensional electron gas (2DEG). Furthermore, spontaneous and piezoelectric polarization-induced surface and interface charges can be used to develop very sensitive but robust sensors to detect gases, polar liquids and mechanical pressure. AlGaN/GaN HEMT structures have been demonstrated to exhibit large changes in source–drain current upon exposing the gate region to various block co-polymer solutions. Pt-gated GaN Schottky diodes and Sc2O3/AlGaN/GaN metal-oxide semiconductor diodes also show large change in forward currents upon exposure to H2. Of particular interest is detection of ethylene (C2H4), which has strong double bonds and hence is difficult to dissociate at modest temperatures. Apart from combustion gas sensing, the AlGaN/GaN heterostructure devices can be used as sensitive detectors of pressure changes. In addition, large changes in source–drain current of the AlGaN/GaN HEMT sensors can be detected upon adsorption of biological species on the semiconductor surface. Finally, the nitrides provide an ideal platform for fabrication of surface acoustic wave (SAW) devices. The GaN-based devices thus appear promising for a wide range of chemical, biological, combustion gas, polar liquid, strain and high temperature pressure-sensing applications. In addition, the sensors are compatible with high bit-rate wireless communication systems that facilitate their use in remote arrays.

https://iopscience.iop.org/article/10.1088/0953-8984/16/29/R02/pdf

GaN-based diodes and transistors for chemical, gas, biological and pressure sensing

DRAM cell arrays having a cell area of about 4F 2 comprise an array of vertical transistors with buried bit lines and vertical double gate electrodes. The buried bit lines comprise a silicide material and are provided below a surface of the substrate. The word lines are optionally formed of a silicide material and form the gate electrode of the vertical transistors. The vertical transistor may comprise sequentially formed doped polysilicon layers or doped epitaxial layers. At least one of the buried bit lines is orthogonal to at least one of the vertical gate electrodes of the vertical transistors.

DRAM layout with vertical FETs and method of formation

In a method of manufacturing a semiconductor device, a semiconductor layer is patterned to form a source region, a channel region, and a drain region in the semiconductor layer. The channel region extends between the source region and the drain region. Corners of the channel region are rounded by annealing the channel region to form a nano-rod structure. Part of the nano-rod structure is then used as a gate channel. Preferably, a gate dielectric and a gate electrode both wrap around the nano-rod structure, with the gate dielectric being between the nano-rod structure and the gate electrode, to form a transistor device.

Semiconductor nano-rod devices

This article reviews the effects of radiation damage on GaN materials and devices such as light-emitting diodes and high electron mobility transistors. Protons, electrons and gamma rays typically produce point defects in GaN, in contrast to neutron damage which is dominated by more extended disordered regions. Regardless of the type of radiation, the electrical conductivity of the GaN is reduced through the introduction of trap states with thermal ionization energies deep in the forbidden bandgap. An important practical parameter is the carrier removal rate for each type of radiation since this determines the dose at which device degradation will occur. Many studies have shown that GaN is several orders of magnitude more resistant to radiation damage than GaAs, i.e. it can withstand radiation doses of at least two orders of magnitude higher than those degrading GaAs with a similar doping level. Many issues still have to be addressed. Among them are the strong asymmetry in carrier removal rates in n- and p-type GaN and interaction of radiation defects with Mg acceptors and the poor understanding of interaction of radiation defects in doped nitrides with the dislocations always present.

Radiation effects in GaN materials and devices

The present paper proposes an improved charge control model of lattice-mismatched AlGaN/GaN HEMTs, valid over the entire operating region. The model for estimation of two-dimensional electron gas (2-DEG) sheet carrier concentration accounts for the strongly dominant spontaneous and piezoelectric polarization at the AlGaN/GaN heterointerface. The dependence of 2-DEG sheet carrier concentration on the aluminum composition and AlGaN layer thickness has been investigated in detail. Current–voltage characteristics developed from the 2-DEG model include the effect of field dependent mobility, velocity saturation and parasitic source/drain resistances. Close proximity with experimental data confirms the validity of the proposed model.

An accurate charge control model for spontaneous and piezoelectric polarization dependent two-dimensional electron gas sheet charge density of lattice-mismatched AlGaN/GaN HEMTs

A two-dimensional analytical model for an AlGaN/GaN MODFET is presented. The model assumes the velocity saturation of electrons in 2-DEG, which causes current saturation and accurately predicts the output conductance arising from the channel length modulation. The effects of spontaneous and piezoelectric polarization at the AlGaN/GaN heterointerface, the field-dependent mobility, and the parasitic source/drain resistances have been incorporated in the analysis. A good fit with the experimental data is obtained for an Al0.15Ga0.85N/GaN MODFET, thus proving the validity of our model. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 117–123, 2001.

2‐D analytical model for current–voltage characteristics and output conductance of AlGaN/GaN MODFET

A new technique is proposed to optimise the device parameters of a thin-film fully depleted SGT MOSFET to minimise short-channel effects. The model offers new opportunities for realising future ULSI circuits with SGTs.

Optimisation for improved short-channel performance of surrounding/cylindrical gate MOSFETs

Proposes an accurate model to investigate the small-signal microwave parameters of fully strained (FS) and partially relaxed (PR) Al/sub m/Ga/sub 1-m/N/GaN high electron-mobility transistors (HEMTs). It is observed that elastic strain relaxation of the Al/sub m/Ga/sub 1-m/N layer imposes an upper limit on the maximum two-dimensional electron-gas sheet charge density and is, thus, extremely critical in determining the microwave performance of high Al-content Al/sub m/Ga/sub 1-m/N/GaN HEMTs. The model incorporates the effects of strain relaxation of the barrier layer, field-dependent mobility, parasitic source/drain resistance, and velocity saturation to evaluate drain current, transconductance, drain conductance, cutoff frequency, and transit time of FS and PR Al/sub m/Ga/sub 1-m/N/GaN HEMTs with different Al mole fractions. The proposed model predicts a high drain current of 5.94 A/mm for a PR 0.3-/spl mu/m Al/sub 0.4/Ga/sub 0.6/N/GaN HEMT, which is in close proximity with previously published simulated results. A peak transconductance of 154 mS/mm is also estimated for a 1-/spl mu/m gate-length device with aluminum concentration of 15% (FS), which is in close agreement with previously published measured data. A high cutoff frequency of 21.09 GHz was predicted for a 0.6-/spl mu/m device with an Al mole fraction of 0.5 (PR), thus showing the potential of AlGaN/GaN HEMTs for microwave applications.

Comprehensive analysis of small-signal parameters of fully strained and partially relaxed high Al-content lattice mismatched Al/sub m/Ga/sub 1-m/N/GaN HEMTs

An improved charge-control model for the dc and microwave characteristics of an Al0.15Ga0.85N/GaN modulation-doped FET (MODFET) is developed. The effect of piezoelectric polarization-induced charge at the AlGaN/GaN heterointerface has been incorporated. The small-signal microwave parameters have been evaluated to determine the current–gain cutoff frequency (ft). High current levels (503.4 mA/mm), large gm (160 mS/mm), and high ft (9.48 GHz) are achieved for a 1 μm Al0.15Ga0.85N/GaN MODFET. The results so obtained are in close agreement with experimental data. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 413–419, 2000.

Analytical model for dc characteristics and small‐signal parameters of AIGaN/GaN modulation‐doped field‐effect transistor for microwave circuit applications

Rashmi

Papers

An accurate charge control model for spontaneous and piezoelectric polarization dependent two-dimensional electron gas sheet charge density of lattice-mismatched AlGaN/GaN HEMTs

2‐D analytical model for current–voltage characteristics and output conductance of AlGaN/GaN MODFET

Optimisation for improved short-channel performance of surrounding/cylindrical gate MOSFETs

Comprehensive analysis of small-signal parameters of fully strained and partially relaxed high Al-content lattice mismatched Al/sub m/Ga/sub 1-m/N/GaN HEMTs

Analytical model for dc characteristics and small‐signal parameters of AIGaN/GaN modulation‐doped field‐effect transistor for microwave circuit applications