Hole Generation in Polarization‐Doped AlxGa1–xN (x = 0.9–0.35)‐Graded Layer with Heavily Mg‐Doped Al0.35Ga0.65N Contact Layer for 275 nm Deep‐Ultraviolet Light‐Emitting Diode

Herein, hole generation in a 60 nm thick polarization‐doped Al x Ga 1– x N ( x = 0.9–0.35)‐graded layer with some Mg doping (5 × 10 18 cm −3 ) is demonstrated by using a 10 nm thick heavily (1 × 10 20 cm −3 ) Mg‐doped Al 0.35 Ga 0.65 N contact layer. First, light emission from a deep‐ultraviolet light‐emitting diode is observed with the Al x Ga 1– x N ( x = 0.9–0.35)‐graded layer and the Al 0.35 Ga 0.65 N contact layer, indicating a vertical hole transport from the Al 0.35 Ga 0.65 N contact layer to the active region through the polarization‐doped AlGaN‐graded layer. Second, hole concentration, mobility, and resistivity values of the Al x Ga 1– x N ( x = 0.9–0.35)‐graded layer and the Al 0.35 Ga 0.65 N contact layer are evaluated by Hall effect measurement. A hole concentration of 1.8 × 10 18 cm −3 is clearly observed by removing the AlGaN contact layer (not underneath of electrodes) to minimize a parallel conduction. The hole concentration shows a very weak temperature dependence from room temperature down to 150 K, suggesting that the holes are generated by polarization doping. Hole generation in the fully strained Al x Ga 1– x N ( x = 0.9–0.35)‐graded layer is directly evaluated by Hall effect measurement with the AlGaN contact layer just underneath the electrodes.