Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors. Contents 1. Introduction 33 2. Photodetector parameters 34 3. Semiconductors for UV photodetection 34 4. SiC photodetectors 36 4.1. Schottky photodiodes 36 4.2. The p-n junction 37 4.3. Charge-coupled devices 37 4.4. Particle detectors 38 5. Diamond photodetectors 38 5.1. Photoconductors 38 5.2. Schottky photodiodes 39 5.3. Metal-semiconductor-metal photodiodes 39 5.4. Phototransistors 39 5.5. X-ray and particle detectors 40 5.6. Photocathodes 40 6. III-nitride photodetectors 40 6.1. Photoconductors 41 6.2. Schottky photodiodes 42 6.3. Metal-semiconductor-metal photodiodes 44 6.4. The p-i-n photodiodes 45 6.5. Avalanche photodiodes 46 6.6. Phototransistors 46 6.7. Photocathodes 46 7. II-VI semiconductors 47 7.1. ZnS, ZnSe and related compounds 47 7.2. ZnO 48 8. Conclusion and perspectives 48

No abstract

We have studied the electronic confinement in hexagonal ͑0001͒ GaN / AlN multiple quantum wells by means of structural ͑high-resolution x-ray diffraction and transmission electron microscopy͒ as well as optical characterizations, namely intersubband absorption and interband photoluminescence spectroscopies. Intense intersubband absorptions covering the 1.33-1.91 m wavelength range have been measured on a series of samples with well thicknesses varying from 1 to 2.5 nm. The absorption line shape exhibits either a pure Lorentzian shape or multiple peaks. In the first case the broadening is homogeneous with a state-of-the-art low value of 67 meV. We deduce a dephasing time of the electrons in the excited subband T 2 of about 20 fs. For structured spectra the absorption can be perfectly reproduced with a sum of several Lorentzian curves; the individual peaks originate from absorption in quantum well regions with thickness equal to an integer number of monolayers. We have also carried out simulations of the electronic structure which point out the relevance of the nonparabolicity and many-body corrections on the intersubband absorption energy. The intersubband absorption exhibits a blue shift with doping as a result of many-body effects dominated by the exchange interaction. An excellent agreement with the experimental data is demonstrated. The best fit is achieved using a conduction band offset at the GaN / AlN heterointerfaces of 1.7± 0.05 eV and a polarization discontinuity ⌬P / ͑⑀ 0 ⑀ r ͒ of 10±1 MV/cm.