In this work, we investigate an unexplored possibility of passivating the charged surface states on AlGaN/GaN high electron mobility transistor (HEMT) heterostructures by using organic molecules. This has further led to remarkable enhancement in the electrical properties of rectifying metal-semiconductor contacts on AlGaN/GaN. Phenol functionalized Zinc metallated-Tetra Phenyl Porphyrin (Zn-TPPOH) organic molecules were adsorbed on AlGaN/GaN via the solution phase to form a molecular layer (MoL). The presence of the MoL was confirmed using X-ray Photoelectron Spectroscopy (XPS). The thickness of the MoL was assessed as ∼1 nm, using Spectroscopic Ellipsometry and cross-sectional Transmission Electron Microscopy. XPS peak-shift analyses together with Kelvin Probe Force Microscopy revealed that the molecular surface modification reduced the surface potential of AlGaN by approximately 250 meV. Consequently, the Barrier height (ideality factor) of Ni Schottky diodes on AlGaN/GaN was increased (reduced) significantly from 0.91 ± 0.05 eV (2.5 ± 0.31) for Ni/AlGaN/GaN to 1.37 ± 0.03 eV (1.4 ± 0.29) for Ni/Zn-TPPOH/AlGaN/GaN. In addition, a noteworthy decrement in the reverse current from 2.6 ± 1.93 μA to 0.31 ± 0.19 nA at −5 V (∼10 000 times) was observed from Current-Voltage (I-V) measurements. This surface-modification process can be fruitful for improving the performance of AlGaN/GaN HEMTs, mitigating the adverse effects of surface states and polarization in these materials.
|Original language||English (US)|
|Journal||Journal of Applied Physics|
|State||Published - Nov 19 2018|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): BAS/1/1664-01-01, URF/1/3437-01-01, REP/1/3189-01-01
Acknowledgements: Manjari Garg is grateful to the Council of Scientific and Industrial Research (CSIR), India, for providing research fellowship. The authors would like to acknowledge Indian Nanoelectronics User Program (INUP) at Indian Institute of Technology Bombay for the molecular chemisorption work and XPS measurements. The authors are also thankful to Professor M. Ravikanth, IIT Bombay, for porphyrin based organic molecules. The authors are also obliged to Nanoscale Research Facility (NRF) at Indian Institute of Technology Delhi for the deposition of Cu and Ni Schottky contacts and for KPFM, Spectroscopic Ellipsometry, and I-V and C-V measurements. The KAUST authors acknowledge the support from KAUST Baseline BAS/1/1664-01-01, KAUST Competitive Research Grant URF/1/3437-01-01, and GCC Grant REP/1/3189-01-01.