We report on the current properties of Al1-x InxN (x approximate to 0.18) layers lattice- matched ( LM) to GaN and their specific use to realize nearly strain- free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state- of- the- art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of ( 1 - 5) x 10(18) cm(-3) and a large Stokes shift (similar to 800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified through the properties of GaN/ AlInN multiple quantum wells ( QWs) suitable for near- infrared intersubband applications. A built- in electric field of 3.64MVcm(-1) solely due to spontaneous polarization is deduced from photoluminescence measurements carried out on strain- free single QW heterostructures, a value in good agreement with that deduced from theoretical calculation. Other potentialities regarding optoelectronics are demonstrated through the successful realization of crack- free highly reflective AlInN/ GaN distributed Bragg reflectors ( R > 99%) and high quality factor microcavities ( Q > 2800) likely to be of high interest for short wavelength vertical light emitting devices and fundamental studies on the strong coupling regime between excitons and cavity photons. In this respect, room temperature ( RT) lasing of a LM AlInN/ GaN vertical cavity surface emitting laser under optical pumping is reported. A description of the selective lateral oxidation of AlInN layers for current confinement in nitride- based light emitting devices and the selective chemical etching of oxidized AlInN layers is also given. Finally, the characterization of LM AlInN/ GaN heterojunctions will reveal the potential of such a system for the fabrication of high electron mobility transistors through the report of a high two- dimensional electron gas sheet carrier density ( n(s) similar to 2.6 x 10(13) cm(-2)) combined with a RT mobility mu(e) similar to 1170 cm(2) V-1 s(-1) and a low sheet resistance, R similar to 210 Omega square.

https://iopscience.iop.org/article/10.1088/0022-3727/40/20/S16/pdf

Current status of AlInN layers lattice-matched to GaN for photonics and electronics

AlGaN/GaN high-electron mobility transistors (HEMTs) were fabricated on SiC substrates with epitaxial layers grown by multiple suppliers and methods. Devices with gate lengths varying from 0.50 to 0.09 mum were fabricated on each sample. We demonstrate the impact of varying the gate lengths and show that the unity current gain frequency response (fT) is limited by short-channel effects for all samples measured. We present an empirically based physical model that can predict the expected extrinsic fT for many combinations of gate length and commonly used barrier layer thickness (tbar) on silicon nitride passivated T-gated AlGaN/GaN HEMTs. The result is that even typical high-aspect-ratio (gate length to barrier thickness) devices show device performance limitations due to short-channel effects. We present the design tradeoffs and show the parameter space required to achieve optimal frequency performance for GaN technology. These design rules differ from the traditional GaAs technology by requiring a significantly higher aspect ratio to mitigate the short-channel effects.

Short-Channel Effect Limitations on High-Frequency Operation of AlGaN/GaN HEMTs for T-Gate Devices

Wide-bandgap semiconductors are expected to be applied to solid-state lighting and power devices, supporting a future energy-saving society. While GaN-based white LEDs have rapidly become widespread in the lighting industry, SiC- and GaN-based power devices have not yet achieved their popular use, like GaN-based white LEDs for lighting, despite having reached the practical phase. What are the issues to be addressed for such power devices? In addition, other wide-bandgap semiconductors such as diamond and oxides are attracting focusing interest due to their promising functions especially for power-device applications. There, however, should be many unknown phenomena and problems in their defect, surface, and interface properties, which must be addressed to fully exploit their functions. In this review, issues of wide-bandgap semiconductors to be addressed in their basic properties are examined toward their ?full bloom?.

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Wide-bandgap semiconductor materials: For their full bloom†

A systematic study of GaN-based heterostructure field-effect transistors with an insulating carbon-doped GaN back barrier for high-voltage operation is presented. The impact of variations of carbon doping concentration, GaN channel thickness, and substrates is evaluated. Tradeoff considerations in on-state resistance versus current collapse are addressed. Suppression of the off-state subthreshold drain-leakage currents enables a breakdown voltage enhancement of over 1000 V with a low on-state resistance. Devices with a 5-μm gate-drain separation on semi-insulating SiC and a 7-μm gate-drain separation on n-SiC exhibit 938 V and 0.39 mΩ·cm2 and 942 V and 0.39 m Ω·cmcm2, respectively. A power device figure of merit of ~ 2.3 × 109 V2/Ω·cm2 was calculated for these devices.

AlGaN/GaN/GaN:C Back-Barrier HFETs With Breakdown Voltage of Over 1 kV and Low $R_{\scriptscriptstyle{\rm ON}} \times A$

Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now available on the commercial market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper reviews the current state of the art in active switching device performance for both SiC and GaN. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. The SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. Power module demonstrations are beginning to appear in scientific reports and real applications. A short review is therefore given. Other advantages of SiC is the possibility of high temperature operation (> 300 °C) and in radiation hard environments, which could offer considerable system advantages.

SiC power devices — Present status, applications and future perspective

Crack-free AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on a 200 mm Si substrate by metal–organic chemical vapor deposition (MOCVD) is presented. As grown epitaxial layers show good surface uniformity throughout the wafer. The AlGaN/GaN HEMT with the gate length of 1.5 µm exhibits a high drain current density of 856 mA/mm and a transconductance of 153 mS/mm. The 3.8-µm-thick device demonstrates a high breakdown voltage of 1.1 kV and a low specific on-resistance of 2.3 mΩ cm2 for the gate–drain spacing of 20 µm. The figure of merit of our device is calculated as 5.3×108 V2 Ω-1 cm-2.

https://iopscience.iop.org/article/10.7567/APEX.6.026501/pdf

Uniform Growth of AlGaN/GaN High Electron Mobility Transistors on 200 mm Silicon (111) Substrate

We report the fabrication of AlGaN/GaN high electron mobility transistor (HEMT) with high breakdown voltage by employing the metal-insulator-semiconductor (MIS) gate structure. SiO2, SiN, and TiO2 were used for the insulators. The gate leak current was significantly reduced by employing the MIS structure, and the breakdown voltage characteristics were improved. The breakdown voltage of the MIS–HEMTs increased non-linearly with the increase of gate-drain length Lgd. The TiO2 insulator exhibited highest breakdown voltage of 2 kV with the on-resistance of 15.6 mΩ cm2 for Lgd = 28 μm. On the other hand, the breakdown voltage and on-resistance for SiN MIS–HEMT were found to be 1.7 kV and 6.9 mΩ cm2, respectively. We demonstrated that AlGaN/GaN MIS–HEMTs are promising not only for high speed applications but also for high power switching applications.

High breakdown voltage AlGaN/GaN MIS–HEMT with SiN and TiO2 gate insulator

We report recessed-gate Al2O3/AlGaN/GaN normally-OFF metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) on 8 in. Si. The MOS-HEMTs showed a maximum drain current of 300 mA/mm with a high threshold voltage of +2.4 V. The quite low subthreshold leakage current (~10−8 mA/mm) yielded an excellent ON/OFF current ratio (9 × 108) with a small, stable subthreshold slope of 74 mV/dec. An atomic-layer-deposited Al2O3 layer effectively passivates, as no significant drain current dispersions were observed. A high OFF-state breakdown voltage of 825 V was achieved for a device with a gate-to-drain distance of 20 µm at a gate bias of 0 V.

https://iopscience.iop.org/article/10.7567/APEX.7.041003/pdf

Yoshiki Yano

Papers

Uniform Growth of AlGaN/GaN High Electron Mobility Transistors on 200 mm Silicon (111) Substrate

High breakdown voltage AlGaN/GaN MIS–HEMT with SiN and TiO2 gate insulator

Normally-OFF Al2O3/AlGaN/GaN MOS-HEMT on 8 in. Si with Low Leakage Current and High Breakdown Voltage (825 V)

Lattice-matched InAlN/GaN two-dimensional electron gas with high mobility and sheet carrier density by plasma-assisted molecular beam epitaxy

Study of carbon concentration in GaN grown by metalorganic chemical vapor deposition