Photoresponse and defect levels of AlGaN/GaN heterobipolar phototransistorgrown on low-temperature AlN interlayer

We report on a visible-blind AlGaN/GaN heterobipolar phototransistor with l ow threading dislocation density, fabricated by organometallic vapor phase epitaxy using the low-temperature interlayer technique. The dark current at room temperature was as low as 34.6 pA/mm(2) at 3 V and the responsivity w as 160 AAV under 0.78 nW/cm(2) illumination. The high-temperature device pe rformance up to 200 degreesC was marked by the exponential evolution of the dark current under the influence of a deep defect near 459 meV. Also, phot oinduced transient spectroscopy between 50 degreesC and 175 degreesC yielde d evidence of defects at about 93 meV, 137 meV and 205 meV energies, which caused a long-lasting photocurrent after weak-intensity illumination.