|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||DD4, Double Heterojunction Metal-Semiconductor-Metal Photodetector Using ZnO/Si Structure
||Tingfang Yen, Juhyung Yun, Sung Jin Kim, Alexander N. Cartwright , Wayne A. Anderson
|On-Site Speaker (Planned)
High photocurrent generation has been obtained by using a ZnO/Si double heterojunction photodetector (DHP) with metal–semiconductor-metal (MSM) structure contact. Two back to back ZnO/Si heterojunctions have been formed with two interdigitated Au/Yb contacts deposited upon ZnO with contact spacing of 2 μm. The I-V curve displayed symmetric MSM characteristics and photocurrent was one magnitude larger for n-ZnO/p-Si and two magnitudes larger for n-ZnO/ n- Si than the sum of photocurrent generated from each monolayer of ZnO and Si at 20V. The high sensitivity of photocurrent has been achieved with n-ZnO/n-Si DHP showing photo to dark current ratio of 5053 and responsivity of 3.13 A/W. Two main reasons for this greatly increased photocurrent are discussed. An avalanche multiplication process occurs when applied voltage exceeds flat band voltage. Thus, under illumination, the device acts like an avalanche photodiode with internal photocurrent gain. The avalanche multiplication was obtained by gain versus bias voltage characteristic for different temperatures. Since the thickness of lightly doped ZnO is much less compared to the heavily doped n-Si, higher built-in electric field in the ZnO regions can separate electron-hole pairs and cause a tunneling current. In addition, photoluminescence result shows less defect emission with ZnO/Si structure than ZnO/SiO<SUB>2</SUB>. Thus, the spectral response result was improved because of better quality of ZnO thin film with ZnO/Si structure, the ZnO acting as a passivation layer for the Si, and larger photon absorption provided by ZnO.