Degradation in InAlN/GaN-based heterostructure field effect transistors: Role of hot phonons

Abstract

We report on high electric field stress measurements at room temperature on InAlN/AlN/GaN heterostructure field effect transistor structures. The degradation rate as a function of the average electron density in the GaN channel (as determined by gated Hall bar measurements for the particular gate biases used), has a minimum for electron densities around 1×1013 cm−2, and tends to follow the hot phonon lifetime dependence on electron density. The observations are consistent with the buildup of hot longitudinal optical phonons and their ultrafast decay at about the same electron density in the GaN channel. In part because they have negligible group velocity, the build up of these hot phonons causes local heating, unless they decay rapidly to longitudinal acoustic phonons, and this is likely to cause defect generation which is expected to be aggravated by existing defects. These findings call for modified approaches in modeling device degradation.

Limitation of Hot-Carrier Generated Heat Dissipation on the Frequency of Operation and Reliability of Novel Nitride-Based High-Speed HFETs

“…In a similar way, the signature of the resonance has been resolved in an independent experiment on device reliability [8]. The degradation of InAlN/AlN/GaN HFETs caused by a fixed amount of charge transported along the channel at a fixed drain voltage (Fig.…”

“…We measure dependence of hot-phonon lifetime on electron density and supplied electric power [6,[10][11][12] beyond the ranges investigated by other techniques. Nominally undoped InAlN/AlN/GaN gateless structures and HFETs for this project were grown on c-plane semiinsulating GaN:Fe substrates (with a bulk resistivity of ~10 9 -cm) in a low-pressure customdesigned organo-metallic vapor phase epitaxy (OMVPE) system at Virginia Commonwealth University (Richmond, VA) [6][7][8]23]. The growth was initiated with a 250 nm AlN nucleation layer, and followed with a 2-4 m thick undoped GaN layer, a 1-nm-thick undoped AlN spacer layer, and a 18-nm-thick undoped InAlN barrier layer, and finally a ~2-nm-thick GaN cap layer.…”

“…Fluctuations originate at the microscopic level and provide with information on the processes responsible for device operation, reliability, and failure. The novel fluctuation-based approach is impelled by recent demonstration of strong correlation of microwave hot-electron fluctuations with RF performance and degradation of nitride HFETs [6][7][8]. The correlation has its genesis in the dissipation of the so-called longitudinal-optical (LO)-mode heat accumulated by the nonequilibrium LO phonons imprisoned in the channel that hosts the high-density hot-electron gas subjected to a high electric field (Fig.…”

Signature of Hot Phonons in Reliability of Nitride Transistors and Signal Delay

“…2 illustrate that the resonance takes place at ≈ 7×10 12 cm −2 at room temperature, but n res = 1×10 13 cm −2 at a hot-electron temperature of ≈ 1500 K, and n res = 1.4 × 10 13 cm −2 at ≈ 3000 K. Thus, if the 2DEG density in the channel exceeds the resonance value at low electric fields (n > n res ), the channel can be tuned into the resonance through heating of the electron gas [9].…”

“…Device reliability was investigated on a set of nominally identical InAlN/AlN/GaN HFETs prepared from the same wafer [2,13,14]. Drain current was measured as a function of time for the devices biased to the same drain voltage of 20 V and different gate voltages.…”