A. Corrion

Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy

The incorporation of deep level defects in n-type GaN grown by ammonia-based molecular beam epitaxy (MBE) is studied via systematic adjustment of the NH3/Ga flux ratio. Deep level optical and transient spectroscopies, which together enable deep level detection throughout the GaN bandgap, reveal defect states whose individual concentrations vary with the NH3/Ga flux ratio. A general trend of lower concentration for deep levels at EC−3.28, EC−1.28, EC−0.62, and EC−0.25 eV with higher NH3/Ga flux ratio was observed, with the strongest reduction at the EC−0.25 eV level, consistent with expectations for a VN-related defect. The known CN impurity state at EC−3.28 eV and suspected CI-related state at EC−1.28 eV also showed a moderate decrease in concentration at the higher NH3/Ga flux ratio. In contrast, the VGa-related defect at EC−2.62 eV was insensitive to the NH3/Ga flux ratio over the range studied here. Taken together, ammonia-MBE GaN has deep level defects with different sensitivities in flux ratios sugge...

Nonalloyed ohmic contacts in AlGaN/GaN HEMTs by ion implantation with reduced activation annealing temperature

This letter reports AlGaN/GaN high-electron mobility transistors with capless activation annealing of implanted Si for nonalloyed ohmic contacts. Source and drain areas were implanted with an Si dose of 1/spl times/10/sup 16/ cm/sup -2/ and were activated at /spl sim/1260/spl deg/C in a metal-organic chemical vapor deposition system in ammonia and nitrogen at atmospheric pressure. Nonalloyed ohmic contacts to ion-implanted devices showed a contact resistance of 0.96 /spl Omega//spl middot/mm to the channel. An output power density of 5 W/mm was measured at 4 GHz, with 58% power-added efficiency and a gain of 11.7 dB at a drain bias of 30 V.

Unpassivated high power deeply recessed GaN HEMTs with fluorine-plasma surface treatment

In this letter, unpassivated high power deeply recessed GaN-based high electron mobility transistors (HEMTs) are reported. The introduction of a thick graded AlGaN cap layer and a novel fluorine-plasma surface treatment reduced the gate-leakage current and increased breakdown voltage significantly, enabling the application of much higher drain biases. Due to excellent dispersion suppression achieved at an epitaxial level, an output power density of more than 17 W/mm with an associated power added efficiency (PAE) of 50% was measured at 4 GHz and V/sub DS/=80 V without SiN/sub x/ passivation. These results demonstrate the great potential of this novel epitaxial approach for passivation-free GaN-based HEMTs for high-power applications.

Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH3:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH3:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of ∼1.0 nm over 2×2 μm2 atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 μm/h were achieved. TD densities in the buffers as low as 3×109 cm−2 were demonstrated. These buffers were hi...

Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH3:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes—unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting—were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE—both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

Power Performance of AlGaN/GaN HEMTs Grown on SiC by Ammonia-MBE at 4 and 10 GHz

In this letter, we report on the microwave power and efficiency performance of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by ammonia molecular beam epitaxy (ammonia-MBE) on SiC substrates. At 4 GHz, an output power density of 11.1 W/mm with an associated power-added efficiency (PAE) of 63% was measured at V ds = 48 V on passivated devices. At 10 GHz, an output power density of 11.2 W/mm with a PAE of 58% was achieved for V ds = 48 V. These results are the highest reported power performance for AlGaN/GaN HEMTs grown by ammonia-MBE and the first reported for ammonia-MBE on SiC substrates.

Deep-recessed GaN HEMTs using selective etch technology exhibiting high microwave performance without surface passivation

A selective dry etch technology of GaN over AlGaN using BCl₃/SF₆ has been applied to passivation-free deep-recessed GaN HEMTs, significantly reducing the effects of growth and process variations on the device performance, improving reproducibility and manufacturability. The effects of Si delta-doping density on the gate leakage, breakdown voltage and dispersion were investigated. Excellent microwave power performances were achieved without SiN_x passivation. 6 W/mm with PAE of 72% at V_D= 30 V and 11.6 W/mm with PAE of 63% at V_D=50 V were demonstrated at 4 GHz, while 5 W/mm with PAE of 63% at V_D= 28 V and 10.5 W/mm with PAE of 53% at V_D=48 V were obtained at 10 GHz.

Surface Treatment for Leakage Reduction in AlGaN/GaN HEMTs

Development of AIGaN/GaN HEMTs has been largely advanced in recent years, leading to record microwave power performance from solid-state devices. With the AIGaN/GaN HEMTs emerging as a viable technology for high frequency low noise amplifiers and power amplifiers, there are still several problems to be solved. One key problem is the relatively high gate leakage current, which may cause extra noise and reliability problems. In this report, we present a technology which reproducibly reduces gate leakage by two orders without introducing any negative effect on the device performance.

AlGaN/GaN HEMTs with Large Angle Implanted Nonalloyed Ohmic Contacts

In this work we report AIGaN/GaN HEMTs with nonalloyed ohmic contacts by large angle ion implantation with a contact resistance to the channel of 0.2 Omegamm.

AlGaN/GaNHEMT with High PAE and Breakdown Voltage Grown by Ammonia MBE

In this paper, a report on high PAE, high breakdown-voltage HEMTs grown by ammonia MBE is discussed. First, an AlN nucleation layer was grown by plasma-assisted MBE on SiC. Then GaN buffer was grown by ammonia MBE, followed by 30 nm ammonia Al_0.3Ga_0.7N. A sheet charge of 1x10¹³ cm^-2 with a mobility of 1500 cm²V^-1s^-1 was obtained from Hall measurements.