The Electrical Characteristics of ZnO :Ga/p-Si Junction Diode
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The Electrical Characteristics of ZnO :Ga/p-Si Junction Diode Tien-Chai Lin2, Wen-Chang Huang1*, Chia-Tsung Horng1, Shu-Hui Yang1 1 Department of Electro-Optical Engineering, Kun Shan University, No. 949, Da-Wan Road, Yong-Kang district, Tainan, 71003, Taiwan, ROC 2 Department of Electrical Engineering, Kun Shan University, No. 949, Da-Wan Road, YongKang district, Tainan, 71003, Taiwan, ROC *Corresponding author: e-mail:[email protected] ABSTRACT The junction characteristics between ZnO:Ga (GZO) film and p-Si substrate are discussed in the research. For the transparent semiconductor ZnO, the element Ga is chosen to be the dopant source to produce a high quality n-type ZnO thin film. The ZnO:Ga (GZO) film shows a average transmittance is 84.7% (above 400 nm), a bandgap energy of 3.37 eV, a carrier concentration of 7.29×1013 cm-3 and a resistivity of 118 Ω-cm. For the GZO/p-Si junction, it shows a junction barrier height of 0.54 eV with an ideality factor of 1.24. The capacitancevoltage measurement shows that it has a uniform reverse bias depletion layer. The Cheung function is also brought to discussion the diode characteristics. INTRODUCTION Zinc oxide (ZnO) is a wide band gap semiconductor exhibiting many interesting properties making it promising for electro-optical devices [1]. ZnO is a direct band gap material with a bandgap of 3.37 eV and shows more resistance to radiation damage than Si and GaN. Moreover, ZnO has a high exciton binding energy (about 60 meV) making the excitons thermally stable at room temperature. It is an n-type semiconductor due to the non-stoichiometry existing in the excess of Zn [2].While, ZnO can be doped with the appropriate metal atoms, such as Al, Sn, Cd, Ga, In, etc. to increase its conductivity. The Ga element was chose to be the dopant source to produce highly conductive as well as high quality film. The structure of n-ZnO/p-Si junction is based on the application of the n-ZnO film as a practical antireflecting photon-window for Si photodiodes. The thin film, ZnO also is used to be a semiconductor layer and produce a built-in potential barrier at the n-ZnOp-Si junction interface. Because of the wide bandgap of ZnO, low energy photons in the visible range may be collected mainly at the depletion region of the p-Si after they are transmitted through the ZnO. It is interesting that such a simple photodiode structure as the n-ZnO/p-Si has not been widely reported except by a small number of studies to date [3-8]. In order to observe a good photoelectric effects from the photodiode, a good pn junction interface quality for a low leakage current and a good film quality for the light transmission and carrier transport is very important. In the present work, we fabricated the n-ZnOp-Si heterojunction. The Ga element was chose to be the dopant source to produce highly conductive as well as high quality film for ZnO. The junction reliability such as barrier height and ideality factor was discussed. The temperature
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dependent current-voltage (I-V-T) measurement was used to evalu
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