UV VIS OPTOELECTRONICS WITH OXIDES UV ‐ VIS OPTOELECTRONICS WITH OXIDES ADRIAN HIERRO, ELIAS MUÑOZ INSTITUTE OF SYSTEMS BASED ON OPTOELECTRONICS AND MICROTECHNOLOGY ELECTRONICS ENGINEERING DEPT. UNIVERSIDAD POLITECNICA DE MADRID (UPM), MADRID, SPAIN UNIVERSIDAD POLITECNICA DE MADRID (UPM), MADRID, SPAIN A. Nakamura and J. Temmyo Research Institute of Electronics Research Institute of Electronics, Shizuoka University, Hamamatsu Shizuoka University Hamamatsu JOINT JST ‐ MINECO PROJECT, SU ‐ UPM collaboration
From “Wide bandgap semiconductors”, Springer 2007. K. Takahashi, A. Yoshikawa, A. Sandhu, editors. 162 Committee JSPS
Why ZnCdMgO? ZnO ZnO Easy to grow with with different plane orientations High exciton binding energy 60 meV; Excitonic effects at RT ZnO high quality substrates already available for homoepitaxy A variety of nanostructures/shapes easily grown Reactive surfaces and prone to get –OH groups Reactive surfaces and prone to get –OH groups ZnCdO → ZnO → Zn 1 ‐ x Mg x O Potentially , bandgap control from (VIS) 2.2 eV to (UV) 8 eV As an example, from present work, ZnMgO keep WZ structure up to Mg 50% (4.4 eV) g ( ) DIFFICULTIES ‐ to reach high Mg/Cd m fractions while keeping WZ S (NPS) to reach high Mg/Cd m fractions while keeping WZ S (NPS) ‐ to obtain reliable and robust p ‐ type doping ‐ CAN ZnCdMgO NANOSTRUCTURES HELP TO CAN ZnCdMgO NANOSTRUCTURES HELP TO CIRCUNVENT SUCH PROBLEMS ?
outline • RPE ‐ MOCVD growth reactor at SU • ZnCdO nanowires grown on a Sapphire paternned substrate: search for high Cd content • Acceptors in undoped ZnMgO • Typical p ‐ doping results in ZnMgO layers • Acceptors in N ‐ doped ZnMgO A t i N d d Z M O • MQW ZnCdO/p ‐ type SiC green LED MQW nCdO/p type SiC green • Summary/reflections
Zn(Mg,Cd)O:N by RPE ‐ MOCVD A. Nakamura, J. Temmyo, Shizuoka U. Remote plasma Heater 10KHz Plasma spectrum in situ Plasma spectrum in situ RF13 56MH RF13.56MHz Oxygen/Hydrogen O 2 plasma/ H 2 carrier Nitrogen OH substrate O y (arb. units) MeCp 2 Mg susceptor OH (EtCp 2 Mg) H Intensity DEZn O 2 plasma/ N 2 carrier N 2 MBP/RP Growth conditions: N 2 NO DMCd N 2 Pressure: 0.1Torr O 2 H 2 /N 2 Temp: 300-600 o C p 2 2 exhaust 200 300 400 500 600 700 800 Wavelength (nm) Hi hl Highly non-equilibrium growth: ilib i th - radical energy enhances decomposition and doping - WZ type ZnO alloys become available 6
STRUCTURAL and OPTICAL PROPERTIES of ZnCdO NANOCOLUMNS SEM ‐ PL+HRXRD*+microEDX+HRTEM* of ZnCdO nanocolumns *HRTEM/EDX collaboration with ‐ Cd%: x=0, 0.14, 0.27 and 0.45!! ‐ Length 1 ‐ 4 m ‐ Length 1 ‐ 4 m V.Muñoz, U.Valencia, SP V.Muñoz, U.Valencia, SP ‐ Diameter 100 ‐ 200 nm HRTEM RT As ‐ grown Annealed PL 14% Cd y (a.u) 27% Cd ZnO 45% Cd PL Intensity micro ‐ EDX 1.0 1.0 Annealed nanowire 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 Zn 0.8 Con 0.8 Energy (eV) %) centration (at centration (at 0.6 0.6 1. Emission demonstrated down to 2.02 eV Cd 0.4 2. Only wurtzite phase observed even for 0.4 45% Cd, no phase separation! 0.2 0.2 Conc t %) 3. State of the art ZnCdO nanocolumns! Nanowire Nanowire Tip 0.0 0.0 Surface 0.0 0.1 0.2 0.3 0.4 0.5 0.1 0.2 Lenght ( m) Width ( m) Results accepted for publication in Appl.Phys.Lett.
CHARACTERIZATION of ZnMgO (MOCVD) LAYERS (SU) C ‐ V profiles RBS determination of stoichiometry and quality* DARK 1.0 <1120> 5.6%Mg 17 -3 ) 10 0.9 0.9 m N d -N a ) (cm alized yield d 0.8 14.5%Mg 18.0%Mg 9.5%Mg 0.7 Norma n= ( N 0.6 Zn a-plane 16 0.5 10 Mg MgZnO MgZnO 0 15 0.15 0 30 0.30 0.45 0 45 0.60 0 60 O O 0.4 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Depth ( m) Theta (º) *Collaboration with A. Redondo, ITN, Portugal Zn 1-x Mg x O 1 O rich behavior of samples 1 . O ‐ rich behavior of samples DLOS + Lighted CV profiling E C 2.Growth plane (a ‐ plane or c ‐ plane) does not affect Mg incorporation Mg n=(N d -N a ) E v +280 meV E v +580 meV (cm -3 ) (cm -3 ) (cm -3 ) (%) 3. ZnMgO is highly compensated 3 ZnMgO is highly compensated 8.02x10 16 1.08x10 17 1.66x10 16 5.6 due to two acceptor levels related E v + 580 meV 9.5 1.98x10 16 3.44x10 17 1.54x10 16 V Zn (-/2-) * to V Zn E v + 280 meV 14.5 1.47x10 16 8.62x10 17 2.27x10 16 V Zn (0/-) * 4. Can use ZnMgO samples to 4. Can use ZnMgO samples to 18 0 18.0 1 27 10 16 1.27x10 16 1.01x10 18 1 01 10 18 5 23 10 16 5.23x10 16 E E V achieve p ‐ type doping Same V Zn related acceptors also found in MBE ZnMgO layers from JM Chauveau, CNRS ‐ CRHEA, FR * A.F. Kohan et al. Phys.Rev.B 61, 15019 (2000)
Typical p ‐ doping results A. Nakamura, J. Temmyo, Shizuoka U. n-type n-type p-type p-type MgZnO:(N,In,Cu) co-doping g ( , , ) p g showed p-type - N solubility enhanced by codoping - (N) O acceptor activated (N) acceptor activated against expectation: - n-type conductivity for N, Cu n type conductivity for N, Cu - Conductivity-type change for N, In was occurred under RTA activation. ref: morphology change after RTA 200nm 200nm As grown RTA 800 o C S. Mohanta, et al. J. Appl. Phys 110 (2011) 013524. 9
N ‐ implantation in MOCVD ZnMgO LAYERS * Implanted profile (SRIM) Implanted profile (SRIM) Crystal recovery (RBS) Crystal recovery (RBS) Optical emission (PL) Optical emission (PL) 0.40 4000 (b) Mg x Zn 1- x O (as grown) 150 keV N 10º + RBS/C 2 MeV He 0.35 3500 =140º, Q=5 C on Å x =15% 0.30 As implanted 3000 x =9% .) s) Yield (counts +500 C (10 ) +500 ºC (10') Vacancies / io Zn nsity (a.u 0.25 Zn+O x =5% 2500 +700 ºC (10') +900 ºC (10') 0.20 x =0% 2000 Random Zn 0.15 1500 O O Y V PL inten 0 10 0.10 1000 Al (c) Mg x Zn 1-x O:N (+RTA 900ºC) 0.05 500 (b) 0.00 0 0 100 200 300 400 500 400 600 800 1000 1200 1400 1600 Depth (nm) Depth (nm) Energy (keV) *Collaboration with A. Redondo, ITN, Portugal CV profiling using Schottky diodes p f g g y 3.3 3.4 3.5 3.6 1E18 5 % Mg Photon energy (eV) As implanted 9 % Mg 1. N implantation at 150 keV -3 ) Implanted + RTA Implanted + RTA m N d -N a (cm 2. Implanted films are highly n ‐ type 1E17 3. Best crystal recovery found at 900°C (strong Al out ‐ diffusion from substrate at higher T). 4. Thermal annealing reduces Xtal damage, films are h l l d l d f l as-grown 1 KHz less n ‐ type, BUT no direct observation of p ‐ type 1E16 0.138 0.207 0.276 0.345 behavior ; defects overcome N ‐ related acceptors W ( m)
MQW ZnCdO/ZnO/p ‐ SiC VIS LED room temprerature Layers grown at Shizuoka U. 5 QW ZnCdO (20% Cd) b. unit) FWHM: 690 meV Mesa: 200 m Mesa: 200 m ensity (arb 80mA EL inte 70 70mA A 60mA 40mA 20mA 1.5 2.0 2.5 3.0 3.5 Photon energy (eV) Rectify ratio: 10 7 @4V -1 10 1. RT CW Emission at unit) -2 2 10 10 2 55 V ( 2.55eV (agreement with i h nsity, L (arb. 2 ) ity (A/cm -3 10 PL from ZnCdO/ZnO -4 10 QW) -5 5 urrent dens 10 grated EL inte 2. First demonstration -6 10 of ZnCdO MQW LED -7 10 in literature!!....green g Integ C -8 10 gap! 0 20 40 60 80 100 -9 10 Injection current, I (m A ) -4 -3 -2 -1 0 1 2 3 4 Results published in IEEE Photon.Tech.Lett.2011 Voltage (V)
SUMMARY • Single-phase wurtzite nanowires of ZnCdO with Cd up to Single-phase wurtzite nanowires of ZnCdO, with Cd up to 50%, have been demonstrated by RPE- MOCVD (C-plane on sapphire) • Single phase wurtzite QW and thick layers of ZnMgO with • Single-phase wurtzite QW and thick layers of ZnMgO with Mg up to 55% have been demonstrated by MBE • Both growth technologies grow quite far from equlibrium B th th t h l i it f f lib i and Zinc vacancies are promoted • Proper growth coditions and substrates seem to allow single phase WZ ZnMgCdO alloys for UV and VIS optoelectronics • In N doped MgZnO alloys (MOCVD) and in N:ZnO (MBE) a shallow acceptor has been detected that seems to correspond to the N O ‐ V Zn complex predicted by N V d t th l di t d b computer simulations and that may play a key role in obtaining robust p-type doping the future of ZnMgCdO alloys for optoelectronics still open….
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