Abstract
(Al + N)-codopedp-type zinc oxide (ZnO)/undopedn-type ZnO homojunction structure was deposited onto Si (100) substrate by using radio frequency (rf) magnetron cosputtering system. Transparent indium tin oxide (ITO)-ZnO cosputtered film was employed as the ohmic contact electrode to then-type ZnO film, and the specific contact resistance was optimized to2.9×10-6 Ω cm2after treating by a rapid thermal annealing (RTA) process at 400°C for 5 min under vacuum ambient. The ohmic contact behavior between the metallic Ni/Au andp-ZnO film also was improved to3.5×10-5 Ω cm2after annealing at 300°C for 3 min under nitrogen ambient. The interfacial diffusion of these ohmic contact systems which led to the optimization of the specific contact resistances by the RTA process was investigated by the Auger electron spectroscopy (AES) depth profile measurements. The diode characteristics of the resultingp-ZnO/n-ZnO homojunction structure realized with these ohmic contact electrodes were confirmed by current-voltage (I-V) measurement, which performed a forward turn-on voltage of 1.44 V with a reverse current of1.1×10-5 A at −2 V.
Highlights
Zinc oxide (ZnO) with a wide and direct band gap (∼3.37 eV) is one of the most promising materials used in shortwavelength optoelectronics applications [1,2,3,4,5]
We demonstrated an (Al + N)-codoped p-type ZnO film Journal of Nanomaterials with a hole concentration higher than 1018 cm−3 using the radio frequency magnetron cosputtering system [15], which is beneficial for developing ZnO-based homojunction structure
For the transparent indium tin oxide (ITO)-ZnO/n-ZnO contact system annealed at 400∘C for 1 min under vacuum ambient, the specific contact resistance was optimized to 2.9 × 10−6 Ω cm2 due to the formation of the homologous Zn2In2O5 compounds associated with the outdiffusion of the oxygen atoms at the n-ZnO layer surface
Summary
Zinc oxide (ZnO) with a wide and direct band gap (∼3.37 eV) is one of the most promising materials used in shortwavelength optoelectronics applications [1,2,3,4,5]. While most ZnO-based optoelectronic devices achieved from the heterojunction structure are in principle superior to those employing homojunction structure, because of the obstacles in obtaining quality and stable p-type ZnO with high conductivity and mobility, there still has been much progress in the preparation of the ZnO-based homojunction structure especially for the light emitting diode applications. Except for the achievement of a quality p-type ZnO film, it is essential to optimize the ohmic contact electrodes to n-type and p-type layers, respectively, since the major loss in device performance is frequently due to high-resistance ohmic contact in case of p-n homojunction structure. With the aim to prepare a ZnO-based homojunction structure with quality diode performance purely using the sputtering technology, the contact resistances for the transparent cosputtered electrode contact to n-type ZnO and Ni/Au metallic system contact to (Al + N) codoped p-type ZnO films, respectively, were firstly optimized by the rapid thermal annealing (RTA) process. A quality ZnO-based homojunction diode based on these ohmic contact systems was achieved as evidence of its rectifying property
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