Donor-Acceptor Complexes in ZnO M. Türker, M. Deicher, H. Wolf, and Th. Wichert Universität des Saarlandes Technische Physik, 66123 Saarbrücken The ISOLDE Collaboration CERN, Geneva, Switzerland

Zinc Oxide EG = 3.37 eV at RT Eexciton binding = 60 meV Bulk crystal Easy to dope n-type Difficult to dope p-type Zn NO O Bulk crystal c-axis N-typ ZnO Anwendung Transparent Conducting Oxide Exziton Bindungsenergy von ZnO is größer als von GaN und hat daher eine höhere Wahrscheinlichkeit zu lasen (laser) ZnO ist günstiger in der Herstellung als GaN EG=3,37eV bei RT gut n-typ, schwer p-typ 2

How to enhance p-type doping? possible In-N2 complex Donor-Acceptor Codoping Yamamoto and Katayama-Yoshida Physica B 302 (2001) 155 Donor-Acceptor Cluster-Doping Wang and Zunger Physical Review Letters 90 (2003) 256401 Zn O NO InZn Inwiefern ist das Bilden solcher Komplexe verantwortlich für die bessere p-Dotierung? Reaktives Sputtern N-doped Resistivity 9x103 OHMcm In-N codoped Resistivity 23.7 OHMcm 3

How to enhance p-type doping? possible In-N2 complex Donor-Acceptor Codoping Yamamoto and Katayama-Yoshida Physica B 302 (2001) 155 Donor-Acceptor Cluster-Doping Wang and Zunger Physical Review Letters 90 (2003) 256401 Zn O NO Electrical properties of ZnO films Sample Carrier type concentration InZn N doped p 3.25  1014 cm-3 In-Nx codoped 3.51  1017 cm-3 increase by factor 1000 Chen, Lu, Ye, Lin, Zhao, Ye, Li, and Zhu Applied Physics Letters 87 (2005) 252106 Inwiefern ist das Bilden solcher Komplexe verantwortlich für die bessere p-Dotierung? Reaktives Sputtern N-doped Resistivity 9x103 OHMcm In-N codoped Resistivity 23.7 OHMcm 3

Codoping with In and N by implantation possible In-N2 complex SIMS depth profiling as implanted TA=1073K t=60min 1020 1019 1018 1017 1016 Zn Concentration [ions/cm3] O NO N In I n InZn In I n N 0.0 0.4 0.8 1.2 0.0 0.4 0.8 1.2 depth [μm] Park, Sakaguchi, Ohashi, Hishita, and Haneda Applied Surface Science 203-204 (2003) 359 Eine Methode, die sensitiv auf die mikroskopisch lokale Umgebung auf atomarer Ebene ist rb112 4 5

Perturbed Angular Correlation (PAC) Electrical field gradient Vij strength Vzz symmetry η = orientation EFG ~ r – 3 - microscopic local Zn Zn Vxx - Vyy Vzz O O NO 111InZn 111InZn EFGlattice EFGdefect Sensitive to microscopic environment d.h. sensitiv auf Störungen in unmittelbarer Nachbarschaft der Sonde, also sensitiv auf In-Defekt Komplexe Proportional to r-3 5 6

Perturbed Angular Correlation (PAC) Donor-acceptor interaction 111In T1/2 = 3 d EC 1 Observation T1/2 = 85 ns Q 2 111Cd Rb112_2 ct002 6 7

Perturbed Angular Correlation (PAC) Donor-acceptor interaction 111In EFG ≠ 0 ω1 ω3 ω2 T1/2 = 3 d EC 1 Observation T1/2 = 85 ns Q 2 111Cd Q = w1= e Q Vzz h 10 3 p Q: quadrupole coupling constant 6 8

Intrinsic EFGlattice of ZnO 111In implantation; TA = 1100K tA = 30min c-axis : R(t) Fourier transforms EFGlattice Q = 31MHz  = 0 f = 86% detector t [ns] w [Mrad/s] 45°-geometry detector rb112 7 9

Codoping of ZnO Indium penetration in ZnO depth 974 Å depth 3368 Å 111In implantation; TA = 1100K tA = 30min R(t) Fourier transforms depth 974 Å EFGlattice Q = 31MHz  = 0 f = 86% E = 400 keV (atoms/cm3) / (atoms/cm2) In t [ns] w [Mrad/s] depth 3368 Å Group V energy penetration depth N 220keV 3368Å P 400keV 3179Å As Sb 400keV 1228Å E = 220 keV (atoms/cm3) / (atoms/cm2) N rb112 8 10

Indium-Nitrogen codoping of ZnO N (220keV) + 111In (400keV); TA = 1000K tA = 20min Q2 Q1 R(t) FT(ω) Q2 Q1 R(t) FT(ω) t [ns] w [Mrad/s] Rb137_06 Rb137_05 9 11

Indium-Nitrogen codoping of ZnO N (220keV) + 111In (400keV); TA = 1000K tA = 20min Q2 2 axial symmetrical EFGdefect: Q1 R(t) FT(ω) c-axis oriented Q1=209(1)MHz =0 f=2% Q2 Q1 basal plane oriented Q2=234(1)MHz ≤0 f=5% R(t) FT(ω) t [ns] w [Mrad/s] w [Mrad/s] Rb137_06 Rb137_05 9 12

Indium-Nitrogen codoping of ZnO Isochronic annealing f0 f2 f1 Rb166: T_M-Reihe Ct009: T_A-Reihe 10 13

Indium-Phosphorus codoping of ZnO P (400keV) + 111In (400keV); TA = 800K tA = 60min Q2 2 axial symmetrical EFGdefect: Q1 R(t) FT(ω) c-axis oriented Q1=153(1)MHz =0 f=2% Q1 Q2 basal plane oriented Q2=176(1)MHz ≤0 f=10% R(t) FT(ω) t [ns] w [Mrad/s] Rb161_02 Rb161_03 11 14

Formation of Indium-Acceptor-Pairs in II-VI semiconductors wurtzite cubic theoretical ZnO *ZnSe *ZnTe *CdTe 111In – N 209 234 271 262 280 111In – P 153 176 219 222 212 111In – As 196 199 186 111In – Sb 169 156 167 **CdTe 274 224 190 162 * Ostheimer, Jost, Filz, Lauer, Wolf, and Wichert Applied Physics Letters 69 (1996) 2840 * * Lany, Ostheimer, Wolf, and Wichert Hyperfine Interactions 136/137 (2001) 619 12 15

Formation of Indium-Acceptor-Pairs in Zinc Oxide Q [MHz] f [%] η Orientation 111In – N 209 (1) 239 (1) 2 5 ≤0.1 c-axis basal plane 111In – P 155 (1) 175 (1) 10 111In – Sb 169 (1) / 9 13 16

Possible configurations of In-NX Complexes ≠0 =0 ≤0.1 In-N3 ≠0 =0 =0 In-N4 14

Summary Donor–acceptor codoping of ZnO by ion implantation Aim: analysis of the microscopic environment on atomic level Tool: Perturbed Angular Correlation to obtain structural information PAC In-N1: 2 EFG In-P1: 2 EFG 15

Work in progress Li Na 77Br K Group VII Group I Donor Acceptor 77Br/ 77Se (60keV); TA = 1100K 77Br Group VII Donor ISOLDE CERN Group I Acceptor Li Na K Q=403 MHz Implantations: Michael Uhrmacher and Daniel Jürgens (U Göttingen) Financial support by BMBF 05KK7TS1 16

InN1-Komplex PAC-Messungen: - 2 axialsymmetrische EFGDefekt =0 ≤0 In-N-Komplex In-P-Komplex - 1 axialsymmetrisches EFGDefekt In-Sb-Komplex

Intrinsic EFGlattice of ZnO 111In diffusion; T = 1400K; t = 4d R(t) Fourier transforms output frequency Q fraction f symmetry orientation c-axis : EFGlattice Q = 31MHz = 0 f = 95% detector 45°-geometry detector ct002 22 7 22

Indium-Nitrogen codoping of ZnO TAnneal-sequence TMeasure-sequence T = 1000K t = 30min Q2 Q2 Q1 Q1 Q0 Q0 f0 f0 f2 f2 f1 f1 Rb166: T_M-Reihe Ct009: T_A-Reihe 10 23

Perturbed Angular Correlation (PAC) 111In PAC time spectra R(t) using the example of polycrystalline ZnO sample T1/2 = 3 d EC R(t) Fourier transforms EFG ≠ 0 ω1 ω3 ω2 1 T1/2 = 85 ns Q 2 111Cd Q = w1= e Q Vzz h 10 3 p Q: quadrupole coupling constant η=0; w1:w2:w3=3:2:1 η: asymmetry parameter Ct021_04 6 24

Indium-Antimon codoping of ZnO Sb (400keV) + 111In (400keV); TA = 900K tA = 30min Q2 1 axial symmetrical EFGdefect: R(t) FT(ω) Q2 basal plane oriented Q2=169(1)MHz ≈0 f=9% R(t) FT(ω) t [ns] w [Mrad/s] 12 25

Perturbed Angular Correlation (PAC) 111In diffusion; T = 1400K; t = 4d R(t) Fourier transforms EFGlattice Q = 31MHz = 0 f = 95% Ct002 rb125 6 26

polykristallin einkristallin Detektor c-Achse Probe c-Achse ^ Detektor Ebene 45°-Geometrie polykristallin einkristallin 27

Implantation 111In (400 keV) 14N (55 keV) 14N (220 keV) 14N (110 keV) TA=1073K t=30min t=60min as implanted TA=1073K t=30min t=60min as implanted 111In (400 keV) Park, Sakaguchi, Ohashi, Hishita und Haneda Applied Surface Science 203-204 (2003) 359-362 14N (55 keV) 14N (220 keV) 14N (110 keV) 28