Pyroelectric and Piezoelectric Properties of GaN-Based Materials
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Abstract We review pyroelectric and piezoelectric properties of GaN-based materials. Pyroelectric effects in GaN have been studied in two different regimes: (i) uniform sample heating regime and (ii) under applied temperature gradient along the sample. The modeling results show that the pyroelectric coefficient, Pv, in GaN (for c-axis along the contacts) can reach 7x105 V/m-K (compared to Pv = 5x105 V/m-K for the best-known high temperature pyroelectric/piezoelectric material LiTaO3). This points to a high potential of GaN-based sensors for high temperature pyroelectronics. Piezoelectric effects strongly affect the performance of electronic and lightemitting devices based on III-N materials. Piezoelectrically induced charge in heterostructures can be as large as 3 to 4x1013 cm-2. Hence, strong lattice polarization effects provide unique possibilities for utilizing GaN-based materials in high temperature piezoelectronics and for their applications in pyroelectric detectors.
Introduction Recent improvements in material quality and contact technology for GaN-based materials system have led to a rapid progress in GaN devices. These devices include blue-green lasers1, blue, green, and amber Light Emitting Diodes2, Ultraviolet (UV) photodetectors3,4, and AlGaN/GaN Heterostructure Field Effect Transistors 5-11. Wide band gap, high peak and saturation velocities, high breakdown voltage and chemical inertness make AlN-GaN-InN based semiconductors an excellent material for solar-blind optoelectronics, and high-power, hightemperature electronics. GaN-based materials are usually grown in the [0001] direction (when they have the wurtzite crystal structure) and in the [111] direction (when they have the zinc blende crystal structure). These are polar axes, and, therefore, GaN-based materials exhibit strong lattice polarization effects. These effects are uniquely suited for applications in high temperature piezoelectronics and for applications in pyroelectric sensors. We report on preliminary studies of pyroelectric properties of GaN. Much (if not most) of the work in this area remains to be done, and we expect dramatic improvements in GaN-based pyroelectric sensors still to come. We discuss the piezoelectric properties of III-Nitrides and the application of the concept of "piezoelectric doping" to GaN-based Heterostructure Field Effect Transistors. We consider the issue of spontaneous polarization in wurtzite GaN, AlN, and InN. Finally, we discuss several unresolved issues and make projections of future progress in GaNbased piezoelectronic devices.
Pyroelectricity in gallium nitride thin films The pyroelectric materials are capable to generate an electric charge in response to heat flow. Heat sources affect the sample temperature by means of thermal convection, thermal diffusion or radiation. Both the primary pyroelectric effect and the secondary pyroelectric effect (piezoelectric effect caused by temperature induced strain) contribute to the pyroelectric response in GaN. The primary pyroelectric effect is dominant under the c
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