Piezoelectric actuation of (GaN/)AlGaN/GaN heterostructures

Abstract

A detailed analysis of the piezoelectric response of (GaN/)AlGaN/GaN heterostructures is reported. The electromechanical properties of two types of heterostructures with an Al content of 31% are compared. Only a single two-dimensional electron gas (2DEG) is formed for samples with thin GaN cap layers, while both a 2DEG and a two-dimensional hole gas coexist in the case of thick GaN caps. The lower GaN layer represents the mechanically supporting layer, while the AlGaN film, and in some cases an additional GaN cap layer, serves as the piezoelectrically active layers for actuation. The 2DEG (at the lower AlGaN/GaN interface) provides the conducting channel which was used as back electrode for the applied external voltage. Electroreflectance spectroscopy is applied in order to determine the electric field distribution across the whole structure as a function of the applied voltage. It is found that only a part of the modulation voltage drops across the active region. Piezoelectric force microscopy yields the field (voltage)-dependent actuation of the layers. By correlating the results of the two experimental techniques we are able to determine the piezoelectric modulus d33 with considerably improved reliability. A value for Al0.31Ga0.69N of 5 pm/V is found which is higher than an estimation based on previously reported data for GaN and AlN

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

“…This result indicates that the internal field in the GaN capping layer increases with the gate voltage, which is contrary to the case of AlGaN barrier layer. It can be explained by the anticlinal energy band bending of GaN capping layer and AlGaN barrier layer [16]. This implies that since the internal electric fields are oppositely directed in the case of the GaN and the AlGaN layers, the corresponding energy bands in each layers should be bent in the opposite direction with applied voltage.…”

The influence of Al content on impurity states in GaN/AlGaN asymmetrically coupled quantum dots

“…It is well known that the wide-band-gap nitride has both wurtzite (WZ) and zinc-blende (ZB) structure phases. Very recently, compared with WZ GaN-based heterostructures, the absence of the built-in electric field is one of the distinguishing physical properties of ZB GaN-based quantum heterostructures [4][5][6][7]. In addition, there is also an increasing interest in ZB GaN QDs due to the improvement that occurs in their growth processes to take advantage of higher saturated electron-drift velocity, easily cleaved cavities for laser diodes and lower band energy in technological applications [8,9].…”

p-doping-free InGaN/GaN light-emitting diode driven by three-dimensional hole gas

“…Note that we have the u-GaN layer under the Al x Ga 1Àx N layer, and thus the electron gas generated below the Al x Ga 1Àx N layer will affect our measurement. [14][15][16] Since C t ¼ C p  C n =ðC p þ C n Þ, in which C t , C p , and C n denote the total capacitance, the capacitance due to the hole depletion, and the capacitance due to the electron accumulation, respectively. When C n ) C p , C t % C p .…”

“…This in turn generates a thin channel in the GaN layer near the GaN/Al x Ga 1Àx N interface where the two-dimensional hole gas (2DHG) can be formed. [14][15][16] The 2DHG can be extended into the three-dimensional hole gas (3DHG) distributing within the Al x Ga 1Àx N layer where the AlN composition is graded to GaN. 10,11 In the previous works (Refs.…”