Deep-UV LEDs using polarization-induced doping: Electroluminescence at cryogenic temperatures

Traditional impurity doping schemes are difficult for extreme-gap semiconductors, such as high Al content AlGaN alloys due to the large activation energies for donors and acceptors. Polarization-induced (or Pi-) doping, since its first demonstration [1], is being gradually implemented as an attractive alternative for effective p-type doping in large-bandgap nitride semiconductors both for power electronics, and for deep-UV photonics. Because mobile carriers are field-ionized instead of thermal ionization, they do not freeze out even at cryogenic temperatures. In this work we demonstrate polarization-induced doping deep-UV LEDs emitting in the 235-260 nm (5.25 to 4.75 eV) spectral range at both room temperature and at cryogenic temperatures. The effectiveness of polarization-induced doping is highlighted by a ~300% increase in the deep-UV EL intensity at 4 K compared to the value at 300 K.