The effect of interdiffusion on strained InGaAs/GaAs quantum-well infrared photodetectors is investigated. Photoluminescence measurements of the interband transition indicate that there is minimal deterioration of the annealed heterostructures, as it is also evident from both the transverse electric and transverse magnetic infrared intersubband optical transitions. The absorption peak wavelength is redshifted from the as-grown 10.2 m to 10.5 and 11.2 m for 5 and 10 s annealing, respectively, at 850°C without appreciable degradation in absorption strength. The peak responsivity of the as-grown and annealed spectra is of comparable amplitude, whereas the annealed spectra become narrower in shape. The dark current of the annealed devices is about an order of magnitude higher than the as-grown one at 77 K.Long-wavelength quantum-well infrared photodetectors ͑QWIPs͒ based on intersubband transitions ͑IT͒ have been quite well studied and are progressing rapidly. 1 With the development of quantum-well ͑QW͒ growth technology and band-gap engineering, high-quality pseudomorphic strainedlayer QWs can be achieved. It has been demonstrated that normal incident strained InGaAs/GaAs QWIPs ͑Ref. 2͒ without grating coupling is possible. Recently, the thermal stability of strained QW layers subjected to heat treatment has been of great interest in the thermal diffusion-induced QW intermixing technique, which can be used to produce tunable operation wavelength optoelectronic devices, 3 especially for structures with higher In concentration. Using this technology, the postgrowth tuning of the AlGaAs/GaAs intersubband absorption peak position 4 and a tunable operation wavelength QWIP ͑Ref. 5͒ have been demonstrated. However, most of the studies have centered on the strain-free AlGaAs/GaAs material system, in which the polarization selection rule requires a nonzero incident light electric-field component along the growth axis. Normal incidence is possible only with an additional optical coupling scheme that increases the complexity of device integration, such as array fabrication. Postgrowth wavelength tuning of a normal incident QWIP without surface grating has yet to be realized. In this letter, we report a wavelength tunable, grating-free, and highly strained normal incident In 0.3 Ga 0.7 As/GaAs QWIP. We demonstrate the postgrowth tunability of the IT absorption peak wavelengths (⌬Ϸ1 m). Both the transverse electric ͑TE͒ and transverse magnetic ͑TM͒ infrared ITs are observed after interdiffusion, indicating that interdiffusion preserves the intrinsic optical characteristic of the strained QWIP material. With the redshift of the detection wavelength, the responsivity is shown to be comparable to the as-grown one by means of QW intermixing.A multiple quantum well ͑MQW͒ was grown by molecular beam epitaxy on a ͑100͒ semi-insulating substrate. Its structure consists of 50 periods of a 40 Å In 0.3 Ga 0.7 As well and a 300 Å GaAs barrier. The QW structure was sandwiched between an n ϩ buffer ͑1 m͒ and a cap layer ͑0.5 m͒ and the wells ...

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We have modeled the dielectric function of wurtzite Al x Ga 1−x N alloys for normal polarization in the energy range up to 10 eV and for all compositions 0 ≤ x ≤ 1. The employed model takes into account one-electron contributions to the dielectric function at E 0 , E 1A , E 1B , and E 1C critical points, as well as excitonic contributions at those critical points. The model is very flexible, due to the use of adjustable broadening function instead of the conventional Lorentzian one. Model parameters are determined by acceptance-probability-controlled simulated annealing. We obtain excellent agreement with the experimental data for all available compositions.