- The photodiode and power meter suitable for measuring the radiation power with high product of internal quantum efficiency (IQE) and external quantum efficiency (EQE) are provided
- Only one photodiode is needed
- The construction and cooling of the detector is simpler
- Radiation measurement
For the purpose of very accurate power determination of photon radiation there exists a technique that is based on the conversion of the photon energy to electrical energy so that the photons of the radiation form electron-hole pairs in the detector, of a solid type. However, there is an existing problem according to which the radiation when hitting the detector normally also yields a diffuse reflection. Even if the radiation were directed in a Brewster angle to the detector surface, some radiation deviates diffusively all around from the hit spot. In very accurate measurements of radiation power, known among the professionals as – absolute radiation power measurement – the diffuse part of the radiation forms an uncertainty factor, if not directly measurable in the particular conditions. One problem relates also to the Internal Quantum Efficiency (IQE) of the material arranged to convert the radiation energy to energy of an electrical current.
Our invention relates to the observation, that the measurement accuracy can be increased. The detector with thick oxide layer on pure silicon body can operate so that the IQE keeps very high within a certain oxide layer thickness range for a wavelength. Also, the invention relates to the improvement of the External Quantum Efficiency (EQE). In our invention an alternative method of Brewster-angle operation for elimination of the effects of reflectance from the photodiode surface is presented. The new detector structure has the advantage that just one photodiode is needed, the construction and cooling of the detector become simpler and elimination of the effect of losses to diffuse reflectance from the photodiode surface is straightforward. Furthermore, we consider methods how the limitation to single useful wavelength in the Brewster-angle operation can be alleviated. In our invention the detectors are expected to be used in vacuum close to liquid Nitrogen temperatures, which enables a much simpler use of technology than in traditional liquid-Helium-cooled cryogenic radiometers.
Technology has been verified successfully.
Priority date: 31.5.2007
Professor Erkki Ikonen
Department of Signal Processing and Acoustics
Head of Innovation Services
Phone: +358 40 186 3320