Velocity Overshoot and Ballistic Electron Transport in Wurtzite Indium Nitride
- PDF / 345,131 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 48 Downloads / 207 Views
ABSTRACT Using an ensemble Monte Carlo approach, ballistic transport and velocity overshoot effects are examined in InN and compared with those in GaN and GaAs. It is found that the peak overshoot velocity is in general greater than both GaN and GaAs. Furthermore, the velocity overshoot in InN occurs over distances in excess of 0.4 im, which is comparable to GaAs but is significantly longer than the overshoot in GaN. These strong overshoot effects, combined with a high peak drift velocity, large low-field mobility, and large saturation drift velocity, should allow InN based field effect transistors to outperform their GaN and GaAs based counterparts. INTRODUCTION GaN has been the focus of attention for its wide band gap and its superior high temperature electrical characteristics [1, 2]. AIN, and its alloys with GaN, have also received attention for their ability to form heterostructures with GaN and serve as wide band gap confining layers in GaN based devices [3, 4]. Recently, 1 um AlGaN/GaN heterostructure field effect transistors (HFETs) with cutoff frequencies, fT, of 18.3 GHz have been demonstrated [5]. A 0.25 jm AIGaN/GaN HFET, with fT equal to 36.1 GHz [6], and a 0.15 ym HFET, with fT equal to 97.3 GHz [7], have also been fabricated. Improvements in material quality and device design are rapidly improving the figures of merit of these devices. InN, and its alloys with GaN, however, have been largely ignored in the design of HFETs, even though their use has been successfully demonstrated in other applications, such as the blue-green laser of Nakamura [8]. In this article, we compare the transient electron transport characteristics of InN with those of GaN and GaAs. We predict that the use of InN in transit time devices could lead to superior performance over current AlGaN/GaN devices. To compare the performance of InN based devices with their GaN and GaAs based counterparts, we use ensemble Monte Carlo simulations and examine electron transit times in these materials. We find that for distances longer than 0.2 jim, the transit times of electrons in InN are less than those of GaN and GaAs due to InN's greater peak drift velocity. By contrast, over shorter distances velocity overshoot effects dominate the transit time. In a previous work [9], we showed that although the low-field mobility of GaN is smaller and its effective mass is heavier than that of GaAs, GaN's ability to operate at large applied
821 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
biases makes the effective velocities higher and the transit times smaller than in GaAs devices. In this work, we show that the larger peak drift velocity of InN in combination with its pronounced velocity overshoot makes the transit times in InN even less than GaN and GaAs. MODEL DESCRIPTION The approach adopted here is similar to that employed in our previous work [9] which compared transient effects in GaN and GaAs. To summarize, a three valley non-parabolic conduction band model is employed. We assume that all donors are ionized, and tha
Data Loading...
