A. T. Winzer

Electroreflectance spectroscopy of Pt/AlGaN/GaN heterostructures exposed to gaseous hydrogen

The effect of hydrogen exposure on the properties of catalytic Pt∕AlGaN∕GaN heterostructures is investigated by electroreflectance spectroscopy. The technique is based on the analysis of the Franz–Keldysh oscillations observed above the AlGaN band gap and yields the electric-field strength in the AlGaN barrier. From these data, the hydrogen-induced changes of the two-dimensional electron gas (2DEG) concentration underneath the catalytic gate contact are quantitatively determined. The exposure increases the 2DEG concentration by 1.7×1012e/cm2 (1.3×1012e/cm2) and decreases the Schottky barrier height by 0.85V (0.65V) for barrier Al contents of 0.15 (0.20).

Stark shift of interband transitions in AlN∕GaN superlattices

The e1h1, e1h2, and e1h3 transitions of AlN∕GaN superlattices with different well widths were detected by electroreflectance measurements in dependence on the externally applied voltage. The quantum confined Stark effect of several tens of meV is observed, whose energy shift increases for larger well widths. The experimental results agree with quantum mechanical calculations at the Brillouin zone center. For well widths of 2.3 and 1.4nm an intrinsic electric field strength in the wells of 5.04 and 6.07MV∕cm is calculated.