The intersubband transition (ISBT) in GaN is expected to be applicable to ultrafast optical devices. By adopting MBE growth and AlN barrier layers. the intersubband absorption in the optical communication wavelength range has been realized. The absorption spectra with a peak wavelength of 1.3-1.5 μm were composed of three Lorentzian components representing t ±1-monolayer thickness variation. The FWHM of the spectral components was 80-100 meV The ISBT wavelengths were strongly affected by the electric field (≥5 MV/cm) caused by the piezoelectric effect and the spontaneous polarization. The measured wavelengths fit well to the theoretical values calculated assuming the field sharing model (a zero-potential drop across one period of the quantum well) and t 1-monolayer graded regions at each hetero interface.
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