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

• 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.

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 2153 ohm/□ at 950 °C, which is 6 times higher than that at 1050 °C (361 ohm/□). 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.