Resonant Cavity Enhancement RCE

The amplification of the radiation at the resonant wavelength in an RCE device and rejection of others results in a increased spectral selectivity of resonant detectors. A logical consequence is an increase of the detector speed [275] which becomes limited by carrier transit time. Another consequence is an increase of the allowed operating temperature because of the shift of the BLIP limit [276]. The high spectral selectivity of RCE detectors may prove advantageous or disadvantageous, depending on the concrete application. 

Interference structures with multiple reflection applied in photodetection were analyzed as early as in 1970s [277]. At the end of 1980s and at the beginning of 1990s the interest for these detectors suddenly increased. It was the result of the requirements for faster photodetectors with narrow spectral range in optical telecommunication, i.e., with minimal crosstalk in wavelength division demultiplexers (WDM). This coincided with the availability of the convenient fabrication technologies [243]. 

RCE structures were used to improve performance of different optoelectronic devices—Schottky diodes [278, 279], p-i-n devices [243], avalanche photodiodes [280], MSM detectors [281], phototransistors [282, 283], LED diodes [284], etc. In the infrared range RCE was used for p-i-n diodes [285], photoconductors [286] and LED diodes [287]. 

The absorptive active region (for MWIR and LWIR devices typically fabricated from a narrow-bandgap material, its thickness d and the absorption coefficient a) is positioned between two layers of wider-bandgap material (thickness Li and and the absorption coefficient of both layers ttex). DBR mirrors are on the top and the bottom side. In some cases the top Bragg mirror does not exist, and its role is assumed by the interface between semiconductor and the incident medium (air), which furnishes a top surface reflection coefficient of about 30 % [251]. 

The consideration of an RCE photodetector reduces to an analysis of a ID microcavity with losses (absorption used for the detection). The interfaces between the DBR mirrors and the wide-bandgap layers are described by the Fresnel complex reflectances rj = ri exp(i /i) and = r2 exp(i /2)- 

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S. Murtaza, K. Anselm, C. Hu, H. Me, B. Streetman, J. Campbell, Resonant-cavity enhanced (RCE) separate absorption and multiplication (SAM) avalanche photodetector (APD). IEEE Photonics Technol. Lett 7(12), 1486-1488 (1995)... 

The second equihbrium group encompasses strucmres for increase in the optical path of the beam which already entered the active area of the detector, the so-called light trapping structures. These structures simultaneously increase radiative lifetime through the mechanism of reabsorption—photon recycling. They include different surface rehef stmctures for the increase in total internal reflection, from diflractive to macroscopic ones. Reflective detector surfaces also belong to this group, both the back-side ones and fuU resonant cavities (RCE—resonant cavity enhancement) with reflective surfaces both of the front and the back side of the detector. The most advanced stmctures for optical path and radiative time increase are radiative shields and photonic crystal enhancement stmcmres, which represent a fuU cavity enhancement and may support the existence of multiple modes. 

It is only to be expected that some nonequilibrium detector stmctures have their analogs in semiconductor lasers. Exclusion detectors correspond to single-hetero-lasers, extraction devices to double-heterolasers, and magnetoconcentration detectors to lasers with the magnetoelectric photoeffect proposed by Marimoto et al. [331]. This inverse analogy is valid not only in electrical, but also in optical field, where e.g., resonant cavity (RCE) detector structures are connected with VCSEL lasers, and lasers with a PBG cavity with PCE (photonic crystal-enhanced) detectors. 

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