| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Friday Sessions |
| Session EM+SS-FrM |
| Session: | Surfaces and Materials for Next Generation Electronics |
| Presenter: | Sriram Krishnamoorthy, Ohio State University |
| Authors: | S. Krishnamoorthy, Ohio State University D.N. Nath, Ohio State University S. Bajaj, Ohio State University S. Rajan, Ohio State University |
| Correspondent: | Click to Email |
The III-Nitride material system has demonstrated its potential for a broad range of optoelectronic and electronic applications. However there are no reports of efficient III-Nitride tunnel junctions due to the large band gaps in this material system. In this work, we show that with unique properties such as the polarization, tunneling can be enhanced using band bending over smaller distances in nitride heterostructures, leading to record reverse and forward tunneling current density for the III-nitride material system.
We have designed and demonstrated GaN/InGaN/GaN tunnel junction with a record high current density of 118 A/cm2 at a reverse bias of 1 V by utilizing a 6.4 nm thin In0.33Ga0.67N barrier material. N-polar p-GaN/In0.33Ga0.67N/n-GaN heterostructure designed for tunneling close to zero bias was grown by plasma assisted molecular beam epitaxy by choosing the critical thickness of InGaN barrier appropriately. The tunnel junction sample shows five orders of magnitude higher current at a reverse bias of 1 V as compared to a standard p+/n+ GaN sample indicating efficient tunneling across the InGaN barrier. The tunneling turn-on close to zero bias, and maximum current density of 9.1 kA/cm2 achieved in this work demonstrates the potential of polarization-engineered tunnel junctions.
Two distinct regimes of transport are identified based on the temperature dependent I-V measurements. At lower reverse bias, defect assisted tunneling with strong temperature dependence is found to dominate. In this regime, a plot of ln (J/E) vs E1/2 shows a linear behavior suggesting a Frenkel- Poole emission mechanism due to the high field in the InGaN quantum well. A direct band to band tunneling regime resulting in weak temperature dependence that arises from band gap variation with temperature is observed from a reverse bias of 1 V. A decrease in current density is observed with increase in temperature in the range of 77- 150 K and this can be attributed to the presence of band tail states which has been observed previously in In face InGaN.
We discuss the design of these quantum well tunnel junctions. Athough higher indium compositions yield higher band to band tunneling probability, calculations using a simplified Kane model reveal that the wider depletion region in n GaN due to higher band offset considerably reduces the net tunneling probability. Calculations also reveal the need for very high doping in the n GaN layer so as to minimize the depletion region thickness in order to achieve very high current densities in such polarization charge assisted tunnel junctions. These calculations can guide future tunnel junctions with better performance characteristics.