Development of Emerging Electronic Devices using Two-Dimensional Materials

Abstract

As the sensor market is growing rapidly, the technologies for the detecting and analyzing of infrared (IR) radiation are being actively investigated. Since most of the current IR detector technologies require a complicated and expensive manufacturing process, there has been consistent effort to improve the performance of the IR detector and to reduce the costs of fabrication. Meanwhile, graphene has been a strong candidate material for the IR photodetector due to its unique and attractive properties for photodetector applications, including fast carrier transit time, variable work function, transparency, etc. However, there have been several challenges for practical use of graphene photodetectors like the instability, the low responsivity, and the large dark current. So many studies have been widely reported to improve the performance of graphene photodetector with various approaches. In this dissertation, the graphene/semiconductor heterostructure is used to enhance the performance of graphene-based photodetectors. In Chapter 1, previous studies on graphene/semiconductor heterostructure are extensively discussed with general introductions about IR photodetectors and graphene photodetectors. In Chapter 2, the graphene/Si Schottky junction with top gate to modulate the Fermi level of graphene is fabricated and its electrical properties are investigated prior to the evaluation of their photodetector performances in followed Chapters. Particularly, the interface properties including the Schottky barrier and the interface trap density (Dit) are examined. Its device performance for future logic applications, which is one of the other application of graphene/semiconductor Schottky junction, is also investigated with semi-empirical device modeling. In Chapter 3, the gate-controlled graphene/Si Schottky junction photodetector for near-infrared (NIR) is demonstrated. It exhibits a high on/off photo switching ratio (~ 104), a very high photoresponsivity (~ 70 A/W), and low dark current. This result is explained by an inherent gain mechanism originating from the difference in carrier transport characteristics of Si and graphene. In Chapter 4, the gate-controlled graphene/Ge Schottky junction photodetector for infrared (IR) is demonstrated. The responsivity of graphene/Ge junction photodetector characterized with scanning photocurrent microscopy (SPCM) system is improved to 0.75 A/W. This result is 5 to 35 times higher value than the previously reported graphene/Ge photodetectors that did not use a gate modulation and the detectivity is also improved by the gate modulation. This improvement is mainly explained by the shift of the quasi-Fermi of graphene under illumination condition.