P-type Oxide Semiconductors for Transparent & Energy Efficient Electronics

  • Zhenwei Wang

Student thesis: Doctoral Thesis


Emerging transparent semiconducting oxide (TSO) materials have achieved their initial commercial success in the display industry. Due to the advanced electrical performance, TSOs have been adopted either to improve the performance of traditional displays or to demonstrate the novel transparent and flexible displays. However, due to the lack of feasible p-type TSOs, the applications of TSOs is limited to unipolar (n-type TSOs) based devices. Compared with the prosperous n-type TSOs, the performance of p-type counterparts is lag behind. However, after years of discovery, several p-type TSOs are confirmed with promising performance, for example, tin monoxide (SnO). By using p-type SnO, excellent transistor field-effect mobility of 6.7 cm2 V-1 s-1 has been achieved. Motivated by this encouraging performance, this dissertation is devoted to further evaluate the feasibility of integrating p-type SnO in p-n junctions and complementary metal oxide semiconductor (CMOS) devices. CMOS inverters are fabricated using p-type SnO and in-situ formed n-type tin dioxide (SnO2). The semiconductors are simultaneously sputtered, which simplifies the process of CMOS inverters. The in-situ formation of SnO2 phase is achieved by selectively sputtering additional capping layer, which serves as oxygen source and helps to balance the process temperature for both types of semiconductors. Oxides based p-n junctions are demonstrated between p-type SnO and n-type SnO2 by magnetron sputtering method. Diode operating ideality factor of 3.4 and rectification ratio of 103 are achieved. A large temperature induced knee voltage shift of 20 mV oC-1 is observed, and explained by the large band gap and shallow states in SnO, which allows minor adjustment of band structure in response to the temperature change. Finally, p-type SnO is used to demonstrating the hybrid van der Waals heterojunctions (vdWHs) with two-dimensional molybdenum disulfide (2D MoS2) by mechanical exfoliation. The hybrid vdWHs show excellent rectifying performance. Due to the ultra-thin nature of MoS2, the operation of hybrid vdWHs is gate-tunable, and we further discover such gate-tunability depends on the layer number of MoS2, i.e., the screening effect. The detailed study in such hybrid vdWHs provides valuable information for understanding the switching performance of junctions contain 2D materials.
Date of AwardMar 11 2018
Original languageEnglish
Awarding Institution
  • Physical Science and Engineering
SupervisorHusam Alshareef (Supervisor)


  • Oxide Semiconductors
  • P-type Oxides
  • Complementary-metal-oxide-semiconductor (CMOS)
  • Transparent electronics

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