Strain-engineered N-Polar GaN HEMTs for High Gain mm-wave Operation
Abstract
In the past years scaled N-polar HEMTs have demonstrated output power densities beyond 8 W/mm and PAEs of 30% at 94 GHz, a breakthrough performance in solid state mm-wave amplifiers. In order to further improve gain and efficiency of these devices we propose to break the material limits of GaN through strain-engineered electron velocity enhancement, an approachwhich has been implemented with remarkable success in silicon. The dominant factor in ft in a well-designed device with reduced parasitics is the transit time in the channel given by the ratio of gate length and the average electron velocity in the channel. We propose to increase the electron velocity in the channel by using a larger lattice constant material, such as relaxed InGaN, as the channel material which provides a reduced electron effective mass, critical in reducing electron scattering and enhancing electron velocity. The 2DEG mobility in an 20%InGaN channel has been predicted to be more than 5000 cm2/Vs as calculated by Yarar et al.. In the absence of InGaN substrates, the relaxed InGaN material will be fabricated using porous GaN. Our recent investigations have shown that InGaN layers on top of porous GaN relax and adopt an in plane lattice constant larger than GaN, a process enabled by the reduced stiffness of porous GaN. Thereby the upper InGaN layers are compliant. Upon consecutive InGaN regrowth,the InGaN lattice constants further increase. In order to serve as base layers for transistors agrowth process for semi-insulating InGaN layers will be developed. A process for the growth of(Al,Ga)N strained to InGaN will be devised as well. Using a pseudo-substrate with 50% InGaNthe fabricated HEMTs are expected to show an ft of over 230GHz and an fmax over 800GHz.We believe that strain engineering is the next major path to enable the demonstration of highperformance III-nitride HEMTs operating in the deep mm-wave spectrum.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 17, 2020
- Source ID
- N000142012138
Entities
People
- Umesh Mishra
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara