Characteristics of GaN/ZrB2 Heterointerfaces Prepared by Pulsed Laser Deposition

Abstract

We have investigated a surface treatment for ZrB2 substrates, and its application to the heteroepitaxial growth of GaN. ZrB2 substrates exhibit atomically-flat terraces with a step-height equal to the c-axis lattice constant after the wet etching in a 0.3% HF solution followed by annealing at 1000 °C under ultra-high vacuum. We have grown 20 nm thick GaN films at various growth temperatures on cleaned ZrB2 substrates using pulsed laser deposition, and have found that high quality GaN grows in the layer-by-layer mode at low substrate temperatures. On the other hand, GaN with poor crystalline quality grows in the three-dimensional growth mode at high growth temperatures. Grazing-incidence angle X-ray reflectivity measurements have revealed that the interfacial layer thickness decreases from 16.2 to 1.0 nm as the growth temperature is reduced from 700 °C to room temperature. These results indicate that a reduction in growth temperature leads to the suppression of interfacial reactions, and makes it possible to take advantage of the small lattice mismatch of 0.6% between GaN and ZrB2.