Raghuraj Hathwar

Demonstration of Diamond-Based Schottky p-i-n Diode With Blocking Voltage > 500 V

Diamond is considered to be the ultimate semiconductor for power devices due to its high breakdown electric field, high carrier mobility, and superior thermal properties. The success of diamond-based electronic devices has been difficult due to critical challenges involved with poor doping efficiency and achievement of ohmic contacts. Achieving n-type diamond has proved to be more difficult over p-type so far. In this letter, we report the achievement of n-type doping in diamond, verified using Hall measurements, which was then used to fabricate Schottky p-i-n diodes measuring a forward current density greater than 300 A/cm2 at 4 V and breakdown voltage of over 500 V with a 3.5-μm -thick drift layer. A Silvaco simulation was performed which agreed well with the experimental data showing turn-ON voltage of 1 V and an ideality factor of 1.04, consistent with the model of a p-i-n diode with a fully depleted n-type contact.

Analysis of the reverse I-V characteristics of diamond-based PIN diodes

Diamond is one of the most promising candidates for high power and high temperature applications, due to its large bandgap and high thermal conductivity. As a result of the growth and fabrication process of diamond-based devices, structural defects such as threading dislocations (TDs) may degrade the electrical properties of such devices. Understanding and control of such defects are important for improving device technology, particularly the reverse breakdown characteristics. Here, we show that the reverse bias current-voltage characteristics in diamond PIN diodes can be described by hopping conduction and Poole-Frenkel emission through TDs over the temperature (T) range of 323 K < T < 423 K, for typical values of the TD density found in epitaxially grown materials.

Temperature dependent simulation of diamond depleted Schottky PIN diodes

Diamond is considered as an ideal material for high field and high power devices due to its high breakdown field, high lightly doped carrier mobility, and high thermal conductivity. The modeling and simulation of diamond devices are therefore important to predict the performances of diamond based devices. In this context, we use Silvaco® Atlas, a drift-diffusion based commercial software, to model diamond based power devices. The models used in Atlas were modified to account for both variable range and nearest neighbor hopping transport in the impurity bands associated with high activation energies for boron doped and phosphorus doped diamond. The models were fit to experimentally reported resistivity data over a wide range of doping concentrations and temperatures. We compare to recent data on depleted diamond Schottky PIN diodes demonstrating low turn-on voltages and high reverse breakdown voltages, which could be useful for high power rectifying applications due to the low turn-on voltage enabling high forward current densities. Three dimensional simulations of the depleted Schottky PIN diamond devices were performed and the results are verified with experimental data at different operating temperatures

Energy Relaxation and Non-linear Transport in InAs Nanowires

Using a full band Monte Carlo simulation the electron energy relaxation times of InAs nanowires along the [100] direction are shown to be greater than the energy relaxation time of bulk InAs. The full band structure and scattering rates of the nanowires are calculated using the sp3d5s* tight binding method and Fermis Golden rule respectively. At moderately high electric fields, a runaway effect is also observed in the nanowires and is attributed to the 1D nature of the scattering rates.

Vertically grown Ge nanowire Schottky diodes on Si and Ge substrates

The processing and performance of Schottky diodes formed from arrays of vertical Ge nanowires (NWs) grown on Ge and Si substrates are reported. The goal of this work is to investigate CMOS compatible processes for integrating NWs as components of vertically scaled integrated circuits, and elucidate transport in vertical Schottky NWs. Vertical phosphorus (P) doped Ge NWs were grown using vapor-liquid-solid epitaxy, and nickel (Ni)-Ge Schottky contacts were made to the tops of the NWs. Current-voltage (I-V) characteristics were measured for variable ranges of NW diameters and numbers of nanowires in the arrays, and the I-V characteristics were fit using modified thermionic emission theory to extract the barrier height and ideality factor. As grown NWs did not show rectifying behavior due to the presence of heavy P side-wall doping during growth, resulting in a tunnel contact. After sidewall etching using a dilute peroxide solution, rectifying behavior was obtained. Schottky barrier heights of 0.3–0.4 V and ...

Carrier relaxation and impact ionization in core-shell III–V nanowires

Nanowires are promising candidates for photovoltaic devices due to their large band gaps and reduced electron-phonon interactions. In the present paper, full band Monte Carlo simulations are performed on square In0.53Ga0.47As nanowires along [100] cladded with InP to study the energy relaxation of carriers in these wires. The carriers are optically excited above the band gap of the cladded nanowire and the energy relaxation times are analyzed for different cladding and core thicknesses. The percentage of carriers undergoing an impact ionization event is also presented.

Modeling of multi-band drift in nanowires using a full band Monte Carlo simulation

We report on a new numerical approach for multi-band drift within the context of full band Monte Carlo (FBMC) simulation and apply this to Si and InAs nanowires. The approach is based on the solution of the Krieger and Iafrate (KI) equations [J. B. Krieger and G. J. Iafrate, Phys. Rev. B 33, 5494 (1986)], which gives the probability of carriers undergoing interband transitions subject to an applied electric field. The KI equations are based on the solution of the time-dependent Schrodinger equation, and previous solutions of these equations have used Runge-Kutta (RK) methods to numerically solve the KI equations. This approach made the solution of the KI equations numerically expensive and was therefore only applied to a small part of the Brillouin zone (BZ). Here we discuss an alternate approach to the solution of the KI equations using the Magnus expansion (also known as “exponential perturbation theory”). This method is more accurate than the RK method as the solution lies on the exponential map and sh...

Full band Monte Carlo simulation of In 0.7 Ga 0.3 As junctionless nanowire field effect transistors

Junctionless nanowire field effect transistors (JNFETs) are promising candidates for the next generation of ultrasmall, low power transistors. In the present paper, three-dimensional simulation results are presented on the performance of junctionless nanowire FETs. A full band Monte Carlo (MC) model is employed, modified to include quantum transport by self consistently solving the Schrodinger equation with a Poisson solver coupled to the full band MC transport equation. The capabilities of the model are demonstrated by simulating the performance of n-type In0.7Ga0.3As junctionless nanowire FETs including subthreshold swing.