Deep levels in MOCVD n-type hexagonal gallium nitride studied by high resolution deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) is performed in MOCVD alpha -GaN e ither doped with two different concentrations of Si or unintentionally dope d. Capacitance transients are measured in Schottky diodes made of an Au or Ni rectifying contact and an Al/Ti ohmic contact, both on the top of the sa mples. Only two peaks are detected in each sample in the energy range from the conduction band edge down to 1.1 eV below it, respectively close to 0.5 0 and 0.92-1.05 eV, by Fourier Transform DLTS (FTDLTS) with concentrations not exceeding 3 x 10(15) cm(-3). These two results testify the high crystal line quality of the samples. The deeper level characteristics depend on the shallow impurity, either Si or the unintentional shallow donor, in deep st ates which comprise in fact a fine structure not evidenced by FTDLTS. A hig h resolution DLTS (HRDLTS) method is implemented to resolve this fine struc ture into several sub-levels which cannot be related to distinct chemical e nvironments. The study of emission and capture kinetics confirms that at le ast three charge states (+,0,-) are involved. It is concluded that MOCVD al pha -GaN comprises deep centers which are stabilized in such a form with a concentration in the range of a few 10(14)-10(15) cm(-3). (C) 2001 Elsevier Science B.V. All rights reserved.