Walid A. Hadi

Steady-state and transient electron transport within the wide energy gap compound semiconductors gallium nitride and zinc oxide: an updated and critical review

The wide energy gap compound semiconductors, gallium nitride and zinc oxide, are widely recognized as promising materials for novel electronic and optoelectronic device applications. As informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within these wide energy gap compound semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving field, in this paper we review analyzes of the electron transport within the wide energy gap compound semiconductors, gallium nitride and zinc oxide. In particular, we discuss the evolution of the field, compare and contrast results determined by different researchers, and survey the current literature. In order to narrow the scope of this review, we will primarily focus on the electron transport within bulk wurtzite gallium nitride, zinc-blende gallium nitride, and wurtzite zinc oxide. The electron transport that occurs within bulk zinc-blende gallium arsenide will also be considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap compound semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, will also be featured. Steady-state and transient electron transport results are presented. We conclude our discussion by presenting some recent developments on the electron transport within these materials. The wurtzite gallium nitride and zinc-blende gallium arsenide results, being presented in a previous review article of ours (O’Leary et al. in J Mater Sci Mater Electron 17:87, 2006), are also presented herein for the sake of completeness.

A transient electron transport analysis of bulk wurtzite zinc oxide

A three-valley Monte Carlo simulation approach is used in order to probe the transient electron transport that occurs within bulk wurtzite zinc oxide. For the purposes of this analysis, we follow O’Leary et al. [Solid State Commun. 150, 2182 (2010)], and study how electrons, initially in thermal equilibrium, respond to the sudden application of a constant applied electric field. We find that for applied electric field strength selections in excess of 300 kV/cm that an overshoot in the electron drift velocity is observed. An undershoot in the electron drift velocity is also observed for applied electric field strength selections in excess of 700 kV/cm, this velocity undershoot not being observed for other compound semiconductors, such as gallium arsenide and gallium nitride. We employ a means of rendering transparent the electron drift velocity enhancement offered by the transient electron transport, and then use the calculated dependence of the peak transient electron drift velocity on the applied electri...

The sensitivity of the steady-state and transient electron transport within bulk wurtzite zinc oxide to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient

Using a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport within bulk wurtzite zinc oxide, and its response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient. We find that while the electron transport associated with zinc oxide is highly sensitive to the crystal temperature and to the non-parabolicity coefficient, it is not very sensitive to the doping concentration. These results suggest that zinc oxide is a competitive material for many of the electron device applications envisioned for its gallium nitride counterpart.

A 2015 perspective on the nature of the steady-state and transient electron transport within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide: a critical and retrospective review

Wide energy gap semiconductors are broadly recognized as promising materials for novel electronic and optoelectronic device applications. As informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within the wide energy gap semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving and burgeoning field of research, we review analyzes of the electron transport within some wide energy gap semiconductors of current interest in this paper. In order to narrow the scope of this review, we will primarily focus on the electron transport that occurs within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide in this review, these materials being of great current interest to the wide energy gap semiconductor community; indium nitride, while not a wide energy gap semiconductor in of itself, is included as it is often alloyed with other wide energy gap semiconductors, the resultant alloys being wide energy gap semiconductors themselves. The electron transport that occurs within zinc-blende gallium arsenide is also considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, is also provided. Steady-state and transient electron transport results are presented. The evolution of the field, and a survey of the current literature, are also featured. We conclude our review by presenting some recent developments on the electron transport within these materials.

Electron transport and electron energy distributions within the wurtzite and zinc-blende phases of indium nitride: Response to the application of a constant and uniform electric field

Within the framework of an ensemble semi-classical three-valley Monte Carlo electron transport simulation approach, we critically contrast the nature of the electron transport that occurs within the wurtzite and zinc-blende phases of indium nitride in response to the application of a constant and uniform electric field. We use the electron energy distribution and its relationship with the electron transport characteristics in order to pursue this analysis. For the case of zinc-blende indium nitride, only a peak corresponding to the electrons within the lowest energy conduction band valley is observed, this peak being seen to broaden and shift to higher energies in response to increases in the applied electric field strength, negligible amounts of upper energy conduction band valley occupancy being observed. In contrast, for the case of wurtzite indium nitride, in addition to the aforementioned lowest energy conduction band valley peak in the electron energy distribution, and its broadening and shifting to...

Transient electron transport in the III-V compound semiconductors gallium arsenide and gallium nitride

A three-valley Monte Carlo simulation approach is used for a detailed comparative analysis of the transient electron transport that occurs within bulk zinc blende gallium arsenide and bulk wurtzite gallium nitride. We find that in both cases that the electron drift velocity and the average electron energy field-dependent “settling times” are strongly correlated, and that the electric field resulting in the shortest electron transit-time is a function of the channel length. The calculated dependence of the peak transient electron drift velocity on the applied electric field can be used for the design optimization of short-channel high-frequency devices.

On the applicability of a semi-analytical approach to determining the transient electron transport response of gallium arsenide, gallium nitride, and zinc oxide

We critically examine the applicability of the semi-analytical approach of Shur (M. Shur, Electron Lett 12, 615 (1976)) in evaluating the transient electron transport response of gallium arsenide, gallium nitride, and zinc oxide. In particular, we contrast results obtained using this semi-analytical approach of Shur with those obtained using Monte Carlo simulations of the electron transport. Our approach will be to examine the response of an ensemble of electrons to the application of a constant and uniform applied electric field. For the purposes of this analysis, three aspects of the transient electron transport response will be considered: (1) the dependence of the electron drift velocity on the time elapsed since the onset of the applied electric field, (2) the dependence of the average electron energy on the time elapsed since the onset of the applied electric field, and (3) the dependence of the average electron displacement on the time elapsed since the onset of the applied electric field. The results obtained show that this semi-analytical approach of Shur produces results that are very similar to those produced using Monte Carlo simulations. Thus, this semi-analytical approach of Shur should be applicable for the treatment of non-uniform and time-varying electric fields, making it a useful tool for the treatment of the transient electron transport response within electron device configurations.

Electron Transport Within III-V Nitride Semiconductors

The III-V nitride semiconductors, gallium nitride, aluminum nitride, and indium nitride, have been recognized as promising materials for novel electronic and optoelectronic device applications for some time now. Since informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within these III–V nitride semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving field, in this paper we review analyses of the electron transport within these III–V nitride semiconductors. In particular, we discuss the evolution of the field, compare and contrast results obtained by different researchers, and survey the more recent literature. In order to narrow the scope of this chapter, we will primarily focus on the electron transport within bulk wurtzite gallium nitride, aluminum nitride, and indium nitride for the purposes of this review. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art III–V nitride semiconductor orthodoxy. Steady-state and transient electron transport results are presented. We conclude our discussion by presenting some recent developments on the electron transport within these materials.