n -type doping and passivation of CuInSe 2 and CuGaSe 2 by hydrogen

An impurity in a semiconductor can have either amphoteric behavior (no net production of electron or holes), or be an energetically deep center (carriers produced only at high temperature), or a shallow center (carriers produced even at low temperature). In most semiconductors (e.g., Si, GaAs, GaP, InP, and ZnSe) hydrogen impurities do not produce free carriers, being instead an amphoretic center; yet hydrogen does dope n-type some oxides such as ${\mathrm{SnO}}_{2}$ and ZnO. We studied theoretically whether or not H could dope chalcopyrite ${\mathrm{I}\ensuremath{-}\mathrm{I}\mathrm{I}\mathrm{I}\ensuremath{-}\mathrm{V}\mathrm{I}}_{2}$ compounds, ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}.$ Based on the first-principles calculations, we find that nonsubstitutionally incorporated hydrogen forms a deep donor in ${\mathrm{CuGaSe}}_{2},$ but a relatively shallow donor in ${\mathrm{CuInSe}}_{2}.$ The interaction of hydrogen with the abundant defect complex ${(2V}_{\mathrm{Cu}}+{\mathrm{In}}_{\mathrm{Cu}}{)}^{0}$ yields an even shallower donor, making ${\mathrm{CuInSe}}_{2}$ n type. In addition, our results show that hydrogen passivates the acceptorlike copper vacancies in both ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2},$ thus eliminating p type behavior. These findings, in conjunction with typical conditions under which ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ are grown, indicate that ${\mathrm{CuInSe}}_{2}$ could be doped n type via hydrogen incorporation, whereas ${\mathrm{CuGaSe}}_{2}$ could not. The reason for the different behavior of ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ towards hydrogen is that in the latter case the conduction-band minimum is at a considerably higher energy than in the former case. Despite this difference in electrical properties, it is predicted that hydrogen can be stored in both ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ via implantation since the implanted hydrogens decorate copper atoms as well as preexisting copper vacancies.