ZnO-based p-n Junctions with p-type ZnO by ZnTe Oxidation
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ZnO-based p-n Junctions with p-type ZnO by ZnTe Oxidation Eliana Kaminska1, Ewa Przezdziecka2, Anna Piotrowska1, Jacek Kossut3, Elzbieta Dynowska2, Witold Dobrowolski2, Adam Barcz1,2 Rafal Jakiela2, Elzbieta Lusakowska2 , Jacek Ratajczak1 1
Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland Institute of Physics, PAS, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 3 Institute of Physics, Polish Academy of Sciences, and ERATO Semiconductor Spintronics Project Al. Lotnikow 32/46, 02-668 Warsaw, Poland 2
ABSTRACT The fabrication and properties of ZnO-based rectifying p-n and p-i-n junctions are reported. ZnO films with p-type conductivity were obtained by oxidation of ZnTe grown by MBE on GaAs substrate. SIMS analysis demonstrated substantial outdiffusion of As from GaAs into ZnO yielding p-type ZnO with hole concentration of 1x1019cm-3. Insulating and n-type ZnO films were deposited by magnetron sputtering. The processing of p-n junctions into device structures involved the formation of mesa geometry and preparation of ohmic contacts to p- and n-type regions. INTRODUCTION ZnO is a multifunctional material possessing unique combination of electrical, acoustooptical and piezoelectric properties with applications such as gas sensors, transparent electrodes and SAW devices. Compared with other semiconductors, ZnO, owing to its large exciton binding energy, high saturation velocity, superior resistance to ionizing radiation and high-energy particles, is expected to compete in the area of opto- and microelectronics. The development of active p-n junction devices, however, has been hindered by difficulty in preparing p-type ZnO. Only a few groups, so far, have reported p-n homojunctions [1-5]. Laser doping [1], hybrid beam deposition [2], ultrasonic spray pyrolisis [3], MBE [4] and pulsed laser deposition [5] with arsenic or phosphorous or nitrogen as acceptor sources were used to grow p-type ZnO layers. We have found that an effective way to produce low resistivity p-type ZnO involves thermal oxidation of Zn-based compounds containing acceptor ions such as Zn3N2 or ZnTe:N [6, 7]. A major concern in the preparation of Zn-based material is the incorporation of hydrogen, which may significantly reduce the effectiveness of p-type doping. In this communication, we report on the fabrication and properties of ZnO p-n junctions, with p-type ZnO synthesized by oxidation ZnTe films grown by molecular beam epitaxy (MBE). ZnO with n-type conductivity was deposited by sputtering. Through optimizing p- and n-type material properties as well as crucial technological steps including surface treatment, controlled chemical etching of ZnO and ohmic contact fabrication we have achieved rectifying junctions. EXPERIMENTAL The starting materials for the fabrication of p-type ZnO were ZnTe and Zn.98Mn.02Te films, 0.15-1 µm thick, grown by MBE in hydrogen-free atmosphere, and doped with nitrogen using
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RF plasma source. (100) oriented SI GaAs wafers with undoped SI ZnTe buffers were used as subs
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