P‐type doping and devices based on ZnO

Abstract

Abstract Both n‐type and p‐type ZnO will be required for development of homojunction light‐emitting diodes (LEDs) and laser diodes (LDs). It is easy to obtain strong n‐type ZnO, but very difficult to create consistent, reliable, high‐conductivity p‐type material. The most natural choice of an acceptor dopant is N, substituting for O, and indeed several groups have been able to obtain p‐type material by such doping. Surprisingly, however, other groups have also been successful with P and As, elements with much larger ionic radii than that of O. Although ZnO substrates are now available, most of the epitaxial p‐type layers so far have been grown on sapphire, or other poorly‐matched materials. The lowest p‐type resistivity obtained up to now is about 0.5 Ω‐cm, which should be sufficient for LED fabrication. In spite of the present availability of p‐type ZnO, very few homojunction LEDs have been reported so far, to our knowledge; however, several good heterojunction LEDs have been demonstrated, fabricated with p‐type layers composed of other materials. One such structure, with fairly strong 389‐nm emission at 300 K, involves n‐type ZnO and p‐type AlGaN, grown on an SiC substrate. Also, an N + ‐ion implanted ZnO layer, deposited by chemical vapor deposition on Al 2 O 3 , exhibits 388‐nm emission at 300 K and could be economical to produce. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)