Effect of growth temperature on the impurity incorporation and material properties of N-polar GaN films grown by metal-organic chemical vapor deposition

Abstract

We have investigated the influence of growth temperature on N-polar GaN epitaxial layers deposited on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The GaN films were grown at various temperatures (1050°C, 1000°C, 950°C, 900°C). The sheet resistivity of the GaN film was 2153ohm/□ at 950°C, which is 6 times higher than that at 1050°C (361ohm/□). Secondary ion mass spectroscopy (SIMS) measurement confirmed that the increase of carbon impurity concentration was responsible for the above phenomena. High-resolution X-ray diffraction (HRXRD), photoluminescence (PL) and Raman measurements showed that the GaN film quality did not deteriorate seriously at low growth temperature, implying that reducing the growth temperature would be a feasible method to obtain highly insulating N-polar GaN films. However, further reducing the growth temperature to 900°C led to the sharp increase of oxygen impurity concentration and the decrease of sheet resistivity. This mechanism is explained in detail.