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

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. •Growth temperature is proved to affect the impurity incorporation in N-polar GaN films.•Sheet resistance of the N-polar GaN film increases by a factor of 6.•HRXRD, PL and Raman measurements confirm that the quality of N-polar GaN film does not deteriorate seriously at low growth temperature.