B. Cui

Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures

Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm2/V s) and sheet charge density (>3×1013 cm−2), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼100 Ω/◻ at room temperature. Fabricated 1.2 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼1.3 A/mm and a peak transconductance of ∼260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented.

Deep traps responsible for hysteresis in capacitance-voltage characteristics of AlGaN∕GaN heterostructure transistors

The origin of hysteresis in capacitance-voltage (C-V) characteristics was studied for Schottky diodes prepared on AlGaN∕GaN transistor structures with GaN (Fe) buffers. The application of reverse bias leads to a shift of C-V curves toward higher positive voltages. The magnitude of the effect is shown to increase for lower temperatures. The phenomenon is attributed to tunneling of electrons from the Schottky gate to localized states in the structure. A technique labeled “reverse” deep level transient spectroscopy was used to show that the deep traps responsible for the hysteresis have activation energies of 0.25, 0.6, and 0.9eV. Comparison with deep trap spectra of GaN buffers and Si doped n-GaN films prepared on GaN buffers suggests that the traps in question are located in the buffer layer.

Proton irradiation effects on AlN/GaN high electron mobility transistors

AlN/GaN high electron mobility transistors (HEMTs) were irradiated with 5 MeV protons at fluences from 2×1011 to 2×1015 protons/cm2. Changes from 10% to 35% of the saturation drain current and the source-drain resistances were observed for the HEMTs exposed to the proton irradiations due to radiation-induced carrier scattering and carrier removal. Both forward and reverse bias gate currents were increased after proton irradiation and affected the drain current modulation in the positive gate bias voltage range. There was almost no gate-lag observed for the HEMT exposed to 2×1011 protons/cm2 irradiation and minimal changes for the higher doses, which implied that few surface traps were created by the high energy proton irradiation.

Detection of an endocrine disrupter biomarker, vitellogenin, in largemouth bass serum using AlGaN/GaN high electron mobility transistors

Endocrine disrupters are known to have negative effects on the environment and human health. Real time detection of vitellogenin, an endocrine disrupter biomarker, was demonstrated using AlGaN/GaN high electron mobility transistors (HEMTs). Anti-vitellogenin antibodies were chemically anchored to the gold-coated gate area of the HEMT and immobilized with thioglycolic acid. The potential difference that occurs from the vitellogenin antigen-antibody interaction-induced caused a drain current change in the HEMT. The HEMT sensor was tested for vitellogenin detection both in phosphate buffer saline and largemouth bass serum.

Indium-rich InGaN epitaxial layers grown pseudomorphically on a nano-sculpted InGaN template

Indium-rich InGaN epitaxial layers with a p-i-n structure were grown pseudomorphically on a strain-relaxed InGaN template to reduce structural strain induced by lattice mismatch. We applied a nano-sculpting process to improve the crystal quality of the strain-relaxed InGaN template. The results show that the nano-sculpting process can suppress effectively the threading dislocation generation and improves significantly the I-V characteristic of the InGaN p-i-n structure. This InGaN template technique with nano-sculpting process shows great potential for future applications in indium-rich InGaN optic-electron devices.

Passivation of AlN∕GaN high electron mobility transistor using ozone treatment

Ozone treatment of AlN on AlN∕GaN heterostructures produces effective surface passivation and chemical resistance to the AZ positive photoresist developer used for subsequent device fabrication. The ozone-passivated AlN∕GaN high electron mobility transistors (HEMTs) exhibited low gate leakage currents, high gate modulation voltage, and minimal drain current degradation during gate pulse measurements. With an additional oxygen plasma treatment on the gate area prior to the gate metal deposition, enhancement-mode AlN∕GaN high electron mobility transistors were realized. The gate characteristics of the HEMTs treated with the ozone and oxygen plasma behaved in a manner similar to a metal oxide semiconductor diodelike gate current-voltage characteristic instead of a Schottky diode. Drain breakdown voltages of 23 and 43V for d- and e-mode HEMTs were obtained, respectively. For d-mode HEMTs, there was no reduction in the drain current during the gate pulse measurements at frequencies of 1, 10, and 100kHz. For th...

High-indium-content InGaN quantum-well structure grown pseudomorphically on a strain-relaxed InGaN template layer

A high-indium-content InGaN quantum-well structure was grown on a strain-relaxed InGaN template to reduce structural strain induced by lattice mismatch. The results show that the InGaN template, following a nanosculpting process, can maintain the good crystal quality of the underlying GaN layer and provide a new lattice parameter for pseudomorphically growing a high-indium-content quantum-well structure, and the fourth-order satellite peak of the multi-quantum-well structure is clearly distinguishable. Atom misalignment, a strain gradient, and a composition undulation along the growth direction in the quantum-well structure were not observed by high-resolution transmission electron microscopy and selected area diffraction.