Demonstration of Forward Inter-band Tunneling in GaN by Polarization Engineering

We report on the design, fabrication, and characterization of GaN interband tunnel junction showing forward tunneling characteristics. We have achieved very high forward tunneling currents (153 mA/cm2 at 10 mV, and 17.7 A/cm2 peak current) in polarization-engineered GaN/InGaN/GaN heterojunction diodes grown by plasma assisted molecular beam epitaxy. We also report the observation of repeatable negative differential resistance in interband III-Nitride tunnel junctions, with peak-valley current ratio (PVCR) of 4 at room temperature. The forward current density achieved in this work meets the typical current drive requirements of a multi-junction solar cell.Comment: 3 figure

Polarization-Engineering in III-V Nitride Heterostructures: New Opportunities For Device Design

The role of spontaneous and piezoelectric polarization in III-V nitride heterostructure devices is discussed. Problems as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides are outlined.Comment: 7 pages, 5 figure

Resonant Zener tunnelling via zero-dimensional states in a narrow gap diode

Interband tunnelling of carriers through a forbidden energy gap, known as Zener tunnelling, is a phenomenon of fundamental and technological interest. Its experimental observation in the Esaki p-n semiconductor diode has led to the first demonstration and exploitation of quantum tunnelling in a condensed matter system. Here we demonstrate a new type of Zener tunnelling that involves the resonant transmission of electrons through zero-dimensional (0D) states. In our devices, a narrow quantum well of the mid-infrared (MIR) alloy In(AsN) is placed in the intrinsic (i) layer of a p-i-n diode. The incorporation of nitrogen in the quantum well creates 0D states that are localized on nanometer lengthscales. These levels provide intermediate states that act as “stepping stones” for electrons tunnelling across the diode and give rise to a negative differential resistance (NDR) that is weakly dependent on temperature. These electron transport properties have potential for the development of nanometre-scale non-linear components for electronics and MIR photonics

Experimentally validated quantum transport models for tunneling devices based on novel materials

The desire to reduce the power consumption of consumer electronics has driven the semiconductor industry to seek smaller transistors and to operate them at lower supply voltages. A reduction in the transistors dimensions by a certain fraction can reduce the power consumption by the same amount, for a specific operation speed. The semiconductor industry employs a 14nm feature size for its latest technology node and is pushing it down to 10nm. Moreover, reducing the supply voltage can also significantly lower the power consumption. However, the limit on the supply voltage is set by the threshold voltage, which is more than 0.6V given the fundamental limit of 60mV/dec for MOSFETs. Further reduction in supply voltage and consequently power consumption can be achieved with tunneling transistors that can overcome this limit. Tunneling transistors, however, face challenges with low ON current leading to slow performance. The ON current can be boosted by reducing the tunneling distance, either with a tight gate control in 2D materials or with internal piezo-polarization in nitrides. An accurate prediction of the performance of such nanoscale tunneling devices is obtained from experimentally validated quantum transport simulations. Two practical aspects have been added for a realistic prediction; incomplete ionization of doping and scattering effects on confined states in hetero-structures. Such additions have led to better agreements with relevant experimental measurements. The models have been employed to propose likely candidates towards future low power tunneling transistors based on novel materials and designs

Vertical power diodes based on bulk Gallium Nitride: role of semiconductor defects

The objective of this thesis is to detect which are and what role defects have in semiconductors and in particular in gallium nitride devices, through the in-depth analysis of two set of devices based on GaN: diodes realized by polarization-doping and double-heterostructure diodes with resonant tunneling phenomena

Microwave surface resistance of reactively sputtered NbN thin films

The surface resistance of niobium nitride (NBN) thin films was measured at 7.78 and 10.14 GHz in the temperature range of 1.5 to 4.2 K. The films were reactively sputtered on sapphire substrates to a thickness of approximately 1 micron. The surface resistance was determined by measuring the quality factor (Q) of the TE sub 011 mode of a lead-plated copper cavity where the NbN served as one end-cap of the cavity