Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition

Abstract

The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H2O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio=0.55; however, p-type ZnO films with the hole concentration of the order of 1017 cm−3 could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm2/V s and the lowest resistivity of 0.369 Ω cm have been achieved for the specimen fabricated at the VI/II ratio=1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zni) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (VZn) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic defects was further confirmed by low temperature PL measurements conducted at 10 K. Conclusively, the conduction type of undoped ZnO films deposited by AP-MOCVD is resolved by the VI/II ratio used, which causes the formation of various kinds of intrinsic defects, Zni otherwise VZn. p-type ZnO films with the hole concentration in the range of (1.5–3.3)×1017 cm−3 can be achieved with good reproducibility by modulating a VI/II ratio the range 1.0–2.2 for the AP-MOCVD process.