Piezoresistivity of AlxGa1−xN layers and AlxGa1−xN/GaN heterostructures

Abstract

The piezoresistivity of wurtzite AlxGa1−xN layers with different Al contents and electron concentrations grown by plasma induced molecular beam epitaxy is investigated. A strong increase of the piezoresistivity with increasing Al content and decreasing carrier density is observed. The corresponding piezoresistive gauge factor is negative and its absolute value increases from 3.5 to 25.8 if the Al concentration is increased from x=0 to 0.35. The dependence of the piezoresistive effect on the free electron concentration in the epitaxial layers is calculated by a model which compares the strain induced piezoelectric field to an externally applied gate voltage in field effect transistors. In addition, the strain dependence of the channel conductivity in pseudomorphic, undoped AlGaN/GaN high electron mobility transistors containing a polarization induced two-dimensional electron gas close to the heterointerface, is measured. A remarkably high gauge factor of −85 is observed for these devices.

High frequency dynamic bending response of piezoresistive GaN microcantilevers

“…The effect of mechanical strain, on 2DEG density and output characteristics of AlGaN/GaN heterostructure field effect transistors (HFETs), has been reported earlier. [8][9][10][11][12][13][14][15] High gauge factors (>100) have been reported for quasi-static and step bending response, 8,[12][13][14][15] however, the factors contributing to such high values, especially their deviation from much lower theoretical estimates, are poorly understood. Recently, very high gauge factor of À850 was reported for microcantilevers in transient condition, however, the corresponding dynamic response was not studied.…”

Electronics and sensors based on pyroelectric AlGaN/GaN heterostructures – Part B: Sensor applications

“…The observed gauge factor of -85 is approxi-mately three times higher than the highest values reported for 3C-SiC [12]. The inset shows the calculated and measured dependence of the gauge factor for piezoelectric materials, GFP, on carrier density [20]. The resulting strain sensitivity of the channel resistance is significantly higher, leading to a gauge factor of GF = -85 for an inverted HEMT structure, which consists of a heterostructure with N-face polarity and contains a 45 nm thick Al 0.39 Ga 0.61 N barrier as well as a 4 nm GaN cap layer (n 2DEG = 9⋅10 12 cm -2 ), as shown in Fig.…”

“…a gauge factor of -3 was measured. For higher Al-contents, the absolute value of the negative gauge factor increases, up to 25.8 for an Al mole fraction of 35 % (N e~5 ⋅10 17 cm -3 at room temperature), which can be attributed either to the increasing piezoelectric constants or to a reduced density of free carriers [20]. This behaviour is explained in the model of a field effect transistor by considering the strain induced piezoelectric field as an external gate voltage.…”

“…The influence of the piezoelectric properties of AlGaN on the piezoresistive effect has been investigated by variation of the Al-content [20]. The effect of mechanical strain on piezoelectric fields further results in a high strain sensitivity of AlGaN/GaN HEMT structures.…”

Modeling of GaN/AlN heterostructure-based nano pressure sensors

“…[2][3][4][5][6] The stress-induced modulation of the barrier height in AlGaN/GaN structures has been recently investigated, demonstrating potential use of these structures in pressure or stress sensing. [7][8][9][10] Also, portability of a sensor device, one of the prior concerns in sensor applications, can be achieved with recent progress in nano-fabrication techniques. Recent reports on micro pressure sensors based on Al x Ga 1−x N/GaN heterostructures grown on 6H:SiC substrate 7 show that the proposed heterostructure is a promising candidate.…”