Lattice location studies of the “anti-site” impurities As and Sb in ZnO and GaN Motivation 73 As in ZnO 73 As in GaN 124 Sb in GaN Conclusions U. Wahl 1,2, J.G. Correia 1-3, A.C. Marques 2,3, E.Rita 2, J.C. Soares 2, and the ISOLDE collaboration 3 1) Instituto Tecnológico e Nuclear, Sacavém, Portugal 2) Centro de Física Nuclear da Universidade de Lisboa, Portugal 3) CERN-PH, Geneva, Switzerland

Motivation: possible p-type dopants in ZnO Possible simple “chemical” acceptors in ZnO: ZnIaIbOVa Replace Zn by group Ia or Ib or O by group Va

Motivation: possible p-type dopants in ZnO p-type ZnO has been reported following N, P, As, Sb doping P, As and Sb doping problematic due to difference of ionic radii N 3  1.46 ÅN 3  0.16 Å P 3  2.12 ÅP 3  0.44 Å As 3  2.22 ÅAs 3  0.58 Å Sb 3  2.45 ÅSb 3  0.76 Å O 2  1.38 ÅZn 2  0.60 Å  heavy group V elements fit much better substituting for Zn (“anti-site”)! How to explain the heavy group V acceptors? As Zn  2V Zn model: Limpijumnong et al PRL 92 (2004)  What is the lattice site of heavy group V dopants in ZnO? (As Zn -2V Zn ) 0 (As Zn -2V Zn ) 3 

Motivation: “isoelectronic” impurities in GaN Ternary nitrides allow engineering the bandgap of GaN from far UV to visible But: miscibility gap limits growth of GaAsN, GaPN and GaSbN Miscibility gap: e.g. in GaAs x N 1  x x values with 0.01 < x < 0.85 lead to phase separation into GaAs and GaN  can‘t dope GaN with more than 1% As Why?

Experimental: 73 As emission channeling experiments ZnO bulk and GaN thin film single crystal samples: 1. Implant 2  7  cm  2 73 As (t 1/2 =80.3 d) 60 keV, 1 mm  beamspot 2. Recoil during 73 As  73m Ge (0.54 eV) decay much lower than displacement threshold in ZnO (~57 eV) and GaN (~40 eV) 3. Emission channeling uses the 42.3 keV and 52.2 keV conversion electrons from 73m Ge (499 ms) 4. Lattice location done as-implanted and for vacuum annealing sequence (10 min) up to 900°C recoil 0.54 eV

Emission channeling patterns, 73 As 60 keV 2  cm  2 in ZnO, T A =300°C 91% on S Zn u 1  [2113]= 0.11 Å 98% on S Zn u 1  [1101]= 0.13 Å 83% on S Zn u 1  [1102]= 0.11 Å 94% along c-axis u 1  [0001]= 0.13 Å ZnO U. Wahl et al, Phys. Rev. Lett. 95 (2005)

Emission channeling patterns, 73 As 60 keV 2  cm  2 in ZnO, T A =300°C Patterns for S O or interstitial sites do not fit the experimental results! U. Wahl et al, Phys. Rev. Lett. 95 (2005)

Comparison T A =300°C vacuum T A =900°C vacuum U. Wahl et al, Phys. Rev. Lett. 95 (2005)

Fitted fractions of 73 As sites in ZnO as function of T A  As on S Zn sites dominant for all annealing temperatures  less than 5% As on O sites  T A =900°C in vacuum promotes  30% of As from S Zn to interstitial T

We have identified two possible As sites in ZnO:  Red circle and ellipse indicate the two identified As sites and their rms displacements: 0.11  0.13 Å from S Zn 0.2  0.4 Å from T almost perfect Zn sites!

Emission channeling patterns, 7  cm  2 73 As 60 keV in GaN, T A =20°C S Ga sites dominating but fits improve significantly upon including S N sites !

Fitted fractions of 73 As sites in GaN as function of T A  As always occupies Ga as well as N sites  ratio of As Ga : As N ~ 60:40  As is amphoteric in GaN for all annealing temperatures

Emission channeling patterns, 1  cm  Sb (t 1/2 =60 d) 30 keV in GaN S Ga sites are the dominating sites of Sb in GaN  not ideal conditions: 90% of the beam was 124 Cs (t 1/2 =27 s)...   channeling with = 378 keV produces much narrower effects  preliminary data!  not yet background corrected fits: 13% on S Ga and 2% on S N Similar patterns measured in ZnO: S Zn sites are the dominating sites of Sb in ZnO T A =20°C

Conclusions Implanted As in ZnO incorporated up to  90% on substitutional Zn sites As on substitutional O sites < 5% T A = 900°C promotes 30% of As on interstitial T  As O certainly minority defect, of course not definite proof of As Zn -2V Zn acceptor model As in GaN is amphoteric: As Ga : As N  60 : 40  further explanation of miscibility gap in GaAs x N 1  x Preliminary data: Sb Ga in GaN and Sb Zn in ZnO Outlook: 33 P (t 1/2 =25 d) lattice location studies (implanted at IKS Leuven, measured at CERN)