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Department of Materials Science and Engineering, University of Florida, Gainesville FL 32611, USA (2) Department of Chemical Engineering, University of Florida, Gainesville FL 32611, USA (3) Department of Electrical Engineering, National Central University, Chung-Li 32054, Taiwan (4) Sandia National Laboratories, Albuquerque NM 87185, USA (5) Consultant, Stevenson Ranch, CA 91381, USA ABSTRACT The status of understanding of the behavior of hydrogen in GaN and related materials is reviewed. In particular, we discuss the amount of residual hydrogen in MOCVD-grown device structures such as heterojunction bipolar transistors, thyristors and p-i-n diodes intended for high power, high temperature applications. In these structures, the residual hydrogen originating from the growth precursors decorates Mgdoped layers and AlGaN/GaN interfaces. There is a significant difference in the diffusion characteristics and thermal stability of implanted hydrogen between n- and p-GaN, due to the stronger affinity of hydrogen to pair with acceptor dopants and possibly to the difference in H2 formation probability. INTRODUCTION It is our experience that atomic hydrogen readily permeates into GaN during many different device processing steps. The indiffusion is likely to be strongly enhanced by the presence of the high defect density in heteroepitaxial material. Examples of the processes in which hydrogen is incorporated into GaN at low temperatures (< 300 oC) include plasma enhanced chemical vapor deposition of dielectrics (the source of the hydrogen can be the plasma chemistry or erosion of the photoresist mask), boiling in solvents (including water), annealing under H2 or NH3 ambients and wet etching in acid or base solutions (e.g. NaOH, KOH). Secondary Ion Mass Spectrometry (SIMS) profiling after processing with deuterated chemicals to enhance the detection sensitivity show that hydrogen can diffuse into GaN at temperatures as low as 80 oC. The main effect of the hydrogen is passivation (electrical deactivation) of Mg acceptors in p-GaN through formation of neutral Mg-H complexes, which can be dissociated through either minority carrier (electron) injection or simple thermal annealing. There is evidence that all of the acceptor species in GaN, namely Mg, C, Ca and Cd are found to form complexes with hydrogen. In this paper we will summarize what is known about the effects of hydrogen in GaN and discuss new results on the incorporation of hydrogen in electronic device structures. PRESENT STATE OF KNOWLEDGE

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The following information is firmly established for the behavior of hydrogen in GaN.[1-26] 1. GaN(Mg) grown by atmospheric pressure Metal Organic Chemical Vapor Deposition is highly resistive due to formation of neutral Mg-H complexes.[18,21,22] The Mg can be activated (i.e. produce p-