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

• How to achieve very steep vertical GaN crystal plane using TMAH wet etching.
• How to obtain the GaN lateral nanowires by TMAH wet etching and by using ALD HfO2 layer as a sidewall spacer.
• Crystallographic study was performed to formation of the lateral GaN nanowires.

The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the 〈112¯0〉 direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (112¯0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4° when etched along the 〈11¯00〉 direction, which is corresponding to the (11¯01) plane. The GaN lateral nanowires with two different types of cross-sections, Ω-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 〈112¯0〉 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.