Monte Carlo analysis of transient electron transport in wurtzite Zn1−xMgxO combined with first principles calculations

Abstract

Transient characteristics of wurtzite Zn1−xMgxO are investigated using a three-valley Ensemble Monte Carlo model verified by the agreement between the simulated low-field mobility and the experiment result reported. The electronic structures are obtained by first principles calculations with density functional theory. The results show that the peak electron drift velocities of Zn1−xMgxO (x = 11.1%, 16.7%, 19.4%, 25%) at 3000 kV/cm are 3.735 × 107, 2.133 × 107, 1.889 × 107, 1.295 × 107 cm/s, respectively. With the increase of Mg concentration, a higher electric field is required for the onset of velocity overshoot. When the applied field exceeds 2000 kV/cm and 2500 kV/cm, a phenomena of velocity undershoot is observed in Zn0.889Mg0.111O and Zn0.833Mg0.167O respectively, while it is not observed for Zn0.806Mg0.194O and Zn0.75Mg0.25O even at 3000 kV/cm which is especially important for high frequency devices.

High‐Performance BeMgZnO/ZnO Heterostructure Field‐Effect Transistors

“…The transient peak electron drift velocities of MgZnO alloys with Mg contents from 11.1% to 25.0% were calculated to be between 3.7 × 10 7 and 1.3 × 10 7 cm s −1 . [ 8 ] A transient peak drift velocity as high as 2.0 × 10 8 cm s −1 (at 200 kV cm −1 ) was predicted for a MgZnO/ZnO heterostructure with a Mg content of 30.6% in the barrier, while the maximum steady‐state drift velocity was ≈2.0 × 10 7 cm s −1 (at 80 kV cm −1 ). [ 9 ] In regard to experimental studies, a current‐gain cutoff frequency f T of 2.45 GHz in ZnO thin‐film transistors grown by pulsed laser deposition (PLD) with a gate length of 1.2 μm [ 10 ] and 1.75 GHz in MgZnO/ZnO heterostructure field‐effect transistors (HFETs) with a gate length of 1 μm [ 11 ] have been reported in earlier works; unfortunately, both figures correspond to an average electron velocity of the order of only 1 × 10 6 cm s −1 .…”