Lateral GaN nanowire prepared by using two-step TMAH wet etching and HfO2 sidewall spacer

The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the (11 (2) over bar0) direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (11 (2) over bar0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4 degrees when etched along the (1 (1) over bar 00) direction, which is corresponding to the (1 (1) over bar 01) plane. The GaN lateral nanowires with two different types of cross-sections, Omega-shape which is connected to underlying thick buffer layer through very narrow neck region and rectangle shape which is completely separated from underlying buffer layer, were realized with second lateral TMAH wet etching along the (11 (2) over bar0) direction and by using the atomic layer deposited (ALD) HfO2 layer as a sidewall spacer. The shape is dependent on both the height of the second dry-etched GaN sidewall below the HfO2 spacer and the second wet etching time in TMAH solution. It was found that the dangling bond density at the surface of the crystal plane is responsible for the strong lateral anisotropic etching property of the GaN layer in TMAH solution. (C) 2016 Elsevier B.V. All rights reserved.