Electrically active defects in AlGaN alloys grown by metalorganic chemical vapor deposition

We investigated two series of metalorganic chemical-vapor-deposition-grown Al_xGa_1-xN samples with Al compositions x = 0.1 and 0.3 and free electron concentrations 2.4 × 10¹⁷ and 5.2 × 10¹⁷ cm^-3, respectively. Shallow and deep centers were investigated using electrical characterization methods. Capacitance vs. temperature measurements show the presence of a dominant donor level with a binding energy of about 118 meV in the sample with x = 0.1 and 90 meV in the sample with x = 0.3. Moreover, we observe a hysteresis in the capacitance-voltage measurements from the sample with higher x. Deep-level transient spectroscopy measurements show that this long time relaxation phenomenon is caused by the presence of interface defects between Au and the AlGaN layer, which become more significant with increase in x. The high Al mole fraction creates potential fluctuations at the surface of the sample and makes the surface behave as an interfacial layer.