Enhanced thermal stability of the two-dimensional electron gas in GaN∕AlGaN∕GaN heterostructures by Si3N4 surface-passivation-induced strain solidification

Abstract

The plasma-enhanced chemical-vapor-deposited Si3N4 surface passivation layers with high rf (13.56MHz) and low rf (380KHz), were investigated, using the annealing experiment at 500°C in N2 ambient, for their effectiveness in regard to the stability of the two-dimensional electron gas (2DEG) in GaN∕AlGaN∕GaN high-electron-mobility transistor structures. When the unpassivated sample was annealed, as observation using the Hall and high-resolution x-ray diffraction measurements, an irreversible degradation of the 2DEG behavior and a strain relaxation of the AlGaN epilayer occurred. The Si3N4 deposited with high frequency provided superior long-term stability for the sample and showed no change in the 2DEG conductivity and the strain state in AlGaN epilayer after 170h of aging. However, a significant degradation after deposition and a partial recovery of the 2DEG behavior after annealing due to the Si3N4 densification, was found in sample passivated by low-frequency Si3N4. The enhancement of the long-term stability can be explained as a consequence of the strain solidification of the AlGaN epilayer induced by a denser Si3N4 passivation.

The effect of AlN growth time on the electrical properties of Al0.38Ga0.62N/AlN/GaN HEMT structures

“…Large direct band gap, high peak and saturation electron velocity value and high chemical hardness in combination with high polarization-induced electron concentration and relatively high electron mobility value in AlGaN/GaN heterostructures result in an outstanding output performance of AlGaN/ GaN high electron mobility transistors (HEMTs) [1][2][3]. The progress in the performance of the device depends on the improvement in device fabrication and material quality as well as structure design of the device, one of the main focuses of the last being on the increase of two-dimensional electron gas (2DEG) concentration and electron mobility.…”

Mechanism of mobility increase of the two-dimensional electron gas in AlGaN∕GaN heterostructures under small dose gamma irradiation

“…Therefore, different kinds of passivation materials 2-7 ͑mainly concentrated on more effective Si 3 N 4 passivation͒ or cap layers [8][9][10] were investigated to decrease surface trap effect on the formation of two-dimensional electron gas ͑2DEG͒ at the heterostructure interface. In spite of temporary stabilization of surface properties, an additional surface layer causes stress-induced changes in the barrier layer [11][12][13][14] and changes the conditions for the formation of 2DEG as a result of piezoelectric and spontaneous polarization effects. Therefore, additional methods, such as plasma pretreatment, 15,16 were used before passivation to improve the electrical properties of 2DEG.…”

Effects of the passivation of SiN with various growth stoichiometry on the high temperature transport properties of the two-dimensional electron gas in Al Ga1−N/GaN heterostructures

“…In these dielectrics, Si 3 N 4 is the most widely investigated one. Besides, a lot of work have been done to investigate the effect of Si 3 N 4 passivation on the transport properties of the two-dimension electron gas (2DEG) in Al x Ga 1−x N/GaN heterostructures [8][9][10]. The prevalent result is that the 2DEG density increases after Si 3 N 4 passivation, while the 2DEG mobility decreases.…”