Interstitial and substitutional Zn in InP and InGaAsP

Abstract

Closed-ampoule Zn diffusion in InP results in a net acceptor concentration that is much smaller than the Zn concentration. After subsequent annealing of InP in an atmosphere without Zn, the Zn and net acceptor concentrations have become almost identical, due to a decreased Zn concentration and an increased net acceptor concentration. The annealing treatment gives rise to a decreased contact resistivity. The diffusion depth has not changed. Annealing with a SiN cap on the InP surface does not have this effect on the concentrations. These annealing effects also take place in InGaAsP on InP layers. The results can be explained quantitatively by assuming that Zn is incorporated as both substitutional acceptors and interstitial donors and that only the interstitial Zn is driven out by the annealing, owing to its large diffusion coefficient. Profiles calculated with this interstitial-substitutional model can be fitted to experimental profiles assuming Zn to diffuse as singly ionized interstitial donors. This model can also describe earlier reported results on Zn diffusion in n-type InP for which a profile cutoff is found at a depth where the acceptor concentration equals the background donor concentration and in which the acceptor solubility is higher than in undoped InP.

InP nanowire p-type doping via Zinc indiffusion

“…In NWs, however, the effect is pronounced due to the high surface-to-volume ratio. In the earlier research with planar structures, the topmost few hundred nm show reduced carrier concentration compared to deep regions of the crystal 10,15,16 . Therefore, outdiffusion of substitutional Zn might not be negligible with NWs and should be taken into consideration when dealing with diffusion doped NWs.…”

“…As a result, creating ohmic contacts to the p-type InP NWs becomes increasingly difficult the lower the doping 9 . An alternative pathway for doping is indiffusion of dopants from gas phase at high temperatures, which has been extensively studied for thin films [9][10][11][12][13][14][15][16] , but has been applied to NWs only recently for materials including InAs 17,18 , Si 19,20 and ZnO 21 . With diffusion doping, electrical transparency to the NW contacts can be increased significantly via high carrier concentrations near the surface 17,19 .…”

“…Additionally, hydrogen can effectively passivate Zn acceptors 31 . The post-annealing process activates the interstitial Zn i to substitutional positions (Zn s ), and outdiffuses mainly the Zn i and hydrogen 16,28,30 . In addition, a slow loss of Zn s is indicated by a reduced carrier concentration after prolonged (8 h) annealing in earlier work 16 .…”

“…The post-annealing process activates the interstitial Zn i to substitutional positions (Zn s ), and outdiffuses mainly the Zn i and hydrogen 16,28,30 . In addition, a slow loss of Zn s is indicated by a reduced carrier concentration after prolonged (8 h) annealing in earlier work 16 . While the outdiffusion and activation of Zn i (increasing hole concentration) is competing with the outdiffusion of Zn s (reducing hole concentration), the latter is a much slower process and therefore typically negligible.…”

“…Post-annealing is an essential part of the diffusion doping process, since a considerable part of the diffused Zn take interstitial positions (Zn i ), where they can act as donors and compensate the p-type doping 10,12,16,28,30 . Additionally, hydrogen can effectively passivate Zn acceptors 31 .…”