Kuldeep Takhar

Electrically injected ultra-low threshold room temperature InGaN/GaN-based lateral triangular nanowire laser

We have demonstrated an electrically injected ultra-low threshold (8.9 nA) room temperature InGaN/GaN based lateral nanowire laser. The nanowires are triangular in shape and survived naturally after etching using boiling phosphoric acid. A polymethyl methacrylate (PMMA) and air dielectric distributed mirror provide an optical feedback, which together with one-dimensional density of states cause ultra-low threshold lasing. Finite difference eigen-mode (FDE) simulation shows that triangular nanowire cavity supports single dominant mode similar to TE01 that of a corresponding rectangular cavity with a confinement factor of 0.18.

Evolution of field dependent carrier trapping during off-state degradation for GaN based metal oxide semiconductor high electron mobility transistors

We have shown that the off-state degradation in GaN based metal-oxide-semiconductor high electron mobility transistors has three field dependent regimes. We have considered Al 2O 3 and AlO xN y as the gate dielectrics. The degradation is dominated by electron trapping near the drain edge at relatively low electric field; hole trapping followed by structural defects tends to dominate at high electric field. The structural defects may potentially be caused by an inverse piezoelectric effect when the AlGaN/GaN interface may relax partially. The hole trapping, in particular, at moderate to high electric field can lead to an anomalous trend. The off-state drain current bears the signature of the degradation. The transistor performance is found to deteriorate for all the cases independent of the degradation mechanism. The trapping contribution toward the degradation is partially recoverable; however, the structural damage is found to be permanent. It is also observed that both the gate dielectrics qualitatively suffer from the same degradation mechanism with oxynitride high electron mobility transistors showing higher resilience than their oxide counterpart.We have shown that the off-state degradation in GaN based metal-oxide-semiconductor high electron mobility transistors has three field dependent regimes. We have considered Al 2O 3 and AlO xN y as the gate dielectrics. The degradation is dominated by electron trapping near the drain edge at relatively low electric field; hole trapping followed by structural defects tends to dominate at high electric field. The structural defects may potentially be caused by an inverse piezoelectric effect when the AlGaN/GaN interface may relax partially. The hole trapping, in particular, at moderate to high electric field can lead to an anomalous trend. The off-state drain current bears the signature of the degradation. The transistor performance is found to deteriorate for all the cases independent of the degradation mechanism. The trapping contribution toward the degradation is partially recoverable; however, the structural damage is found to be permanent. It is also observed that both the gate dielectrics q...

Geometric contribution leading to anomalous estimation of two-dimensional electron gas density in GaN based heterostructures

We have observed that the estimation of two-dimensional electron gas density is dependent on the device geometry. The geometric contribution leads to the anomalous estimation of the GaN based heterostructure properties. The observed discrepancy is found to originate from the anomalous area dependent capacitance of GaN based Schottky diodes, which is an integral part of the high electron mobility transistors. The areal capacitance density is found to increase for smaller radii Schottky diodes, contrary to a constant as expected intuitively. The capacitance is found to follow a second order polynomial on the radius of all the bias voltages and frequencies considered here. In addition to the quadratic dependency corresponding to the areal component, the linear dependency indicates a peripheral component. It is further observed that the peripheral to areal contribution is inversely proportional to the radius confirming the periphery as the location of the additional capacitance. The peripheral component is found to be frequency dependent and tends to saturate to a lower value for measurements at a high frequency. In addition, the peripheral component is found to vanish when the surface is passivated by a combination of N2 and O2 plasma treatments. The cumulative surface state density per unit length of the perimeter of the Schottky diodes as obtained by the integrated response over the distance between the ohmic and Schottky contacts is found to be 2.75 × 1010 cm−1.We have observed that the estimation of two-dimensional electron gas density is dependent on the device geometry. The geometric contribution leads to the anomalous estimation of the GaN based heterostructure properties. The observed discrepancy is found to originate from the anomalous area dependent capacitance of GaN based Schottky diodes, which is an integral part of the high electron mobility transistors. The areal capacitance density is found to increase for smaller radii Schottky diodes, contrary to a constant as expected intuitively. The capacitance is found to follow a second order polynomial on the radius of all the bias voltages and frequencies considered here. In addition to the quadratic dependency corresponding to the areal component, the linear dependency indicates a peripheral component. It is further observed that the peripheral to areal contribution is inversely proportional to the radius confirming the periphery as the location of the additional capacitance. The peripheral component is fo...

Modified angelov model for an exploratory GaN-HEMT technology with short, few-fingered gates

The GaN-based HEMT has emerged as a leading technology option for high-power and high-frequency applications because of its outstanding electronic properties. Angelov-GaN is one of the most popular compact models for GaN-HEMT devices. However, we observed that the standard Angelov-GaN model is unable to accurately model small gate length and gate width HEMT. In this work, we present a modified version of the Angelov-GaN model that captures dc and ac non-idealities in exploratory technology HEMTs. In order to capture these effects we extend the standard DC model using parametric analysis; for RF modeling, we use the open-short de- embedding technique to capture additional pad parasitic effects. The modelled DC I-V and bias dependent S-parameters are found to be in good agreement with measured experimental data.

Observation of quantum oscillation of work function in ultrathin-metal/semiconductor junctions

Quantization in energy level due to confinement is generally observed for semiconductors. This property is used for various quantum devices, and it helps to improve the characteristics of conventional devices. Here, the authors have demonstrated the quantum size effects in ultrathin metal (Ni) layers sandwiched between two large band-gap materials. The metal work function is found to oscillate as a function of its thickness. The thermionic emission current bears the signature of the oscillating work function, which has a linear relationship with barrier heights. This methodology allows direct observation of quantum oscillations in metals at room temperature using a Schottky diode and electrical measurements using source-measure-units. The observed phenomena can provide additional mechanism to tune the barrier height of metal/semiconductor junctions, which are used for various electronic devices.