We discuss the use of nitric oxide ͑NO͒ gas to dope ZnO p-type films, fabricated using metallorganic chemical vapor deposition ͑CVD͒ reaction of a Zn metallorganic precursor and NO gas. In this reaction, NO gas is used to supply both O and N to form a N-doped ZnO ͑ZnO:N͒ film. Auger electron spectroscopy analysis indicated that, under Zn-rich condition, the N concentration in the film is readily detectable, with the highest concentration being ϳ3 atom %. For concentrations greater than 2 atom %, the films are p-type. The carrier concentration varies from 1.0 ϫ 10 15 to 1.0 ϫ 10 18 cm Ϫ3 and the mobility is approximately 10 Ϫ1 cm 2 V Ϫ1 s Ϫ1 . The minimum film resistivity achieved is ϳ20 ⍀ cm.ZnO, an optically transparent material, is widely used in various applications such as light-emitting diodes ͑LEDs͒, flat-panel displays, and solar cells. Recently, significant efforts have been made to produce p-type ZnO. However, due to asymmetric doping limitations, ZnO can easily be doped n-type, but is difficult to dope p-type. 1 Reports have emerged indicating some success with N doping of ZnO. [2][3][4][5] In these, high temperature plasma and codoping techniques have been used to assist N doping and activation. The hole concentration achieved varied between 10 16 and 10 19 cm Ϫ3 , but the hole mobilities remained low ͑2 to 0.07 cm 2 V Ϫ1 s Ϫ1 ).Recently, Yan and co-workers have proposed a model predicting that NO gas should be a better N dopant source than N 2 O or N 2 . 6 Their model indicates that the defect formation energy of N on an oxygen site (N O ) from NO should be lower than that from N 2 O. Furthermore, in the case of Zn-rich growth conditions, the defect formation energy of N should be negative. Therefore, under these thermodynamically favorable conditions, forming the N O defect should not require adding energy ͑e.g., high temperature or plasma͒ during deposition.In this paper, we discuss the fabrication of p-type ZnO films using NO gas as the dopant source, without the use of co-dopants or a plasma. ZnO films with clear p-type behavior were made by CVD reaction of a Zn metallorganic precursor and NO gas. We achieved ZnO film with hole concentrations from 1.0 ϫ 10 15 to 1.0 ϫ 10 18 cm Ϫ3 and mobilities of approximately 10 Ϫ1 cm 2 V Ϫ1 s Ϫ1 .
ExperimentalThe experiments were performed using a low-pressure metallorganic chemical vapor deposition ͑LP-MOCVD͒ system made by CVD Equipment Co. ͑Ronkonkoma, NY͒. The deposition temperature was controlled between 200 and 500°C. Ultrahigh-purity diethylzinc ͑DEZ͒ ͑Morton International͒ was used as the Zn source, and N 2 or Ar gas was used as the carrier gas. The chamber pressure was controlled at 30 Torr, and O 2 and NO ͑diluted to 2 vol % in Ar͒ were used as oxidizing and doping sources, respectively.The films were deposited on Corning 1737 glass substrates. The composition of the films was analyzed using ex situ Auger electron spectroscopy ͑AES, Physical Electronics 670 scanning Auger nanoprobe͒. Crystal properties were assessed using X-ray diffraction ͑XRD, Scint...
