ZnO and ZnO-based Heterojunctions Grown by Fast Pulsed Laser Deposition

我們開發一套新的方法來成長晶體薄膜：快速脈衝雷射蒸鍍法。快速脈衝雷射蒸鍍法以固態脈衝雷射 (355 nm wavelength, 15 ns pulse width) 在10 kHz 的頻率下氣化靶材進行蒸鍍。我們成功的利用快速脈衝雷射蒸鍍法在c-Al2O3基板上成長ZnO 薄膜。最佳的ZnO薄膜具有高品質的晶體結構及光學性質。ZnO (0002)面的X-ray繞射顯示薄膜具有高度平行的結晶方向及高度平坦的表面。在光學性質方面，光激發螢光 (photoluminescence) 也顯示低溫時ZnO在雷射光激發下可發出極窄頻寬的螢光。 此外我們還利用快速脈衝雷射蒸鍍法將ZnO蒸鍍在p-type Si基板及預先鍍上AlN buffer layer的p-type Si基板以比較其差異。我們進一步對ZnO/p-Si及 ZnO/AlN/p-Si 兩種異質接面做以下測量：電流-電壓曲線、逆向電流對照光的反應、光激發螢光及電激發螢光，來瞭解異質接面中的電荷傳導機制。Fast pulsed laser deposition (FPLD) process is presented for the epitaxial growth of ZnO thin films, and n-ZnO/p-Si p-n junctions. A diode-pumped solid-state laser (355 nm wavelength, 15 ns pulse width) running at 10 kHz was used to ablate the ZnO target for FPLD process. The ZnO thin films were grown on c-Al2O3 and p-type Si (111) by FPLD. The optimized ZnO film shows high-quality crystal and optical properties. The width of ~10 arcsec in the X-ray ω-scan and distinct pendellösung fringes in the θ-2θ scan of the ZnO (0002) reflection reveal high-quality crystal property. The sharp, ~5 meV width, donor-bound excitons of photoluminescence spectra and higher order (n = 2) free excitons reveal high-quality optical property. Two types of ZnO-based heterojunctions were grown by FPLD, in which intrinsic n-type ZnO films were deposited on p-type Si (111) substrates with or without AlN buffer layer to form p-n junctions. Current-voltage dependence, photoresponse, and electroluminescence were measured to investigate electrical transport mechanism for both heterojunctions.口試委員會審定書...........................................i謝......................................................ii要.....................................................iiibstract..................................................ivontents...................................................vist of figures..........................................viiist of tables.............................................xhapter 1 Introduction.....................................1.1 Introduction to ZnO....................................1.2 Fast pulsed laser deposition system....................4.3 X-ray diffraction......................................5.4 Photoluminescence......................................8eferences................................................10hapter 2 High quality ZnO films grown by fast pulsed laser deposition................................................12 2.1 Introduction....................................12 2.2 ZnO films grown by FPLD.........................13 2.3 PL spectrum of ZnO films........................19 2.4 Electrical properties of the ZnO films..........25 References..........................................27hapter 3 n-ZnO/p-Si Heterojunction.......................29 3.1 Introduction....................................29 3.2 Experiment......................................30.3 ZnO/p-Si growth.......................................30 3.4 I-V behavior....................................35 3.5 Photodiode characters...........................41 3.6 EL performance..................................44 References..........................................50hapter 4 Conclusion......................................5