Low Dislocation Virtual Substrate for Nitride Semiconductors

Field effect transistors (FETs) based on alloys of AlGaN are the current state of the art for the switching and amplification of radio frequency (RF) signals, as would be used in radio communications, RADAR systems, and power conversion and control devices. A significant problem preventing AlGaN-based devices from realizing their true potential is the presence of dislocation defects that result from growing layers of AlGaN on lattice-mismatched substrates. The availability of a low-dislocation, lattice-matched substrate would present significant benefits to the performance and power efficiency of AlGaN devices. Other semiconductor technologies use lattice-matched virtual substrates that are created by depositing thick buffer layers on a suitable, although lattice-mismatched substrate. This approach fails for AlGaN because the predominant dislocation types are sessile under biaxial stress and do not glide to interact and reduce their concentration. We propose that nanometer-scale patterning of the substrate (e.g. AlN, GaN, SiC, Si or sapphire) can induce dislocations to glide and reduce in concentration within the buffer layer. The resulting virtual substrate would have a dislocation density low enough to support the fabrication of high-performance AlGaN FETs and opto-electronic devices.