GaN vertical and lateral polarity heterostructures on GaN substrates
A method to control local GaN polarity on GaN substrates without using Mg-induced inversion has been developed. This method rests on the development of thin alternative inversion layers and the use of the confined epitaxial growth technique to pattern and selectively grow the inversion layer. Used in conjunction with optimized subsequent GaN growth processes, the technique has resulted in structures demonstrating both vertical and lateral polarity inversion on GaN substrates. Scanning electron microscopy shows a smooth interface between regions of different polarities and a smooth surface, the result of equivalent growth rates for both polarities. Electron channeling contrast imaging is used to determine the dislocation density of each region. Transmission electron microscopy (TEM) images show full polarity conversion of the inverted layer. This process enables a wide range of novel variable polarity devices.
► Alternating GaN polarity material has been grown on N-polar GaN substrates.
► An inversion layer (IL) of thin AlN is patterned to selectively invert GaN polarity.
► Interface between polarities is vertical and laterally smooth.
► TEM confirms the IDB between polarities and complete polarity conversion over IL.
► ECCI shows difference in dislocation density between the two polarities.
Fig. 1. ECCI images of (a) Ga-polar region, with threading screw dislocation (TSD) density 1.1×109 cm−2, and (b) N−polar region with TSD density of 8.8×108 cm−2. Examples of threading screw/mixed dislocations are shown with arrows, threading edge dislocations are circled, and step edges are highlighted by dotted lines.
Source: Journal of Crystal Growth