Ultrafast intersubband relaxation (<= 150 fs) in AlGaN/GaN multiple quantum wells

The ultrafast intersubband relaxation in GaN quantum wells has been verifie d. Al0.65Ga0.35N/GaN multiple quantum wells, with as many as 200 wells, wer e grown by optimizing the barrier thickness and introducing GaN intermediat e layers. The intersubband absorption is sufficiently strong for the relaxa tion time to be measured. A pump-probe measurement is performed to investig ate the relaxation. An ultrashort relaxation time of less than 150 fs is ob tained at a wavelength of it 5 mu m. The transient time is shorter than tha t of InGaAs quantum wells by approximately an order of magnitude. This resu lt is promising for realizing ultrafast optical switches. (C) 2000 American Institute of Physics. [S0003-6951(00)02531-6].