Solid state photon counters based on GaAs and GaP materials Josef Blazej, Ivan Prochazka, Karel Hamal Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering, Dept. of Physical Electronics, Brehova 7, 115 19 Prague 1, Czech Republic, blazej@troja.fjfi.cvut.cz SUMMARY We are reporting the first experimental results acquired on solid state photon counters based on GaAs and GaP materials. The semiconductor structures have been operated in a Geiger mode and an active quenched and gated mode and have been employed in a time-correlated photon counting experiment at the wavelengths from X-ray to the near infrared. The dark count rates, photon counting sensitivity and timing resolution have been measured for the experimental diode samples. Keywords: gallium, arsenide, phosphide, photon counting Subject category: New materials and their characterization. INTRODUCTION The solid state photon counters with high timing resolution are of interest of numerous techniques: laser range finding, optical time domain reflectometry, distributed temperature sensors, time resolved spectroscopy, quantum cryptography and others. At present, the most promising technique to detect single photons by use of a solid state detector is an Avalanche Photodiode APD operated in the Geiger mode. In this operating mode the diode is pulse biased above its breakdown voltage; no current is flowing until an avalanche is triggered by an incoming photon or a thermally generated carrier. The current pulse rise time marks the photon’s arrival time. An external electrical circuit, either passive or active, is used to quench the avalanche and to re-apply the bias to the diode. Our previous research and development in the field of single photon avalanche diodes resulted in a large aperture silicon and germanium photon counters with an active quenching circuit well adopted for applications listed above. [1, 2] The temporal resolution of existing silicon or germanium based photon counters is limited by temporal response of avalanche photodiode itself. This limitation is arising from diode construction and material characteristics. For further development of high timing resolution solid state photon counter we are focusing for materials with the higher carrier velocity, the III-V semiconductors are one of the candidates. The gallium based III-V semiconductor material also seems to be promising candidate for detectors operating in the X-ray region. The availability of an all-solid state individual photon counting system with the high timing resolution sensitive in X-ray is strongly demanded as crystalline silicon based detectors degrade when they are exposed to X ray flux. The higher atomic mass of gallium should provide higher detector stability and lifetime. In general, the GaP semiconductor material seems to be the most promising candidate for the detectors operating in the x-ray region That is why we have carried out the first experiments to test the capability of the GaP photon counters to respond to the x-rays. The first experimental samples of the photon counting detectors on the basis of GaAs and GaP semiconductor material have been developed and operated in our labs in last years. [3],[4] DETECTOR CONSTRUCTION To carry out the first experiments, the pre-fabricated structures designed originally for the light emitting applications have been used. Al metal anode AuGeNi metal cathode N P 500 μm SiO2 Al 2 O 3 GaAs N + eff. diam. 350 um Figure 1: The vertical profile of the GaAs avalanche photodiode structure. The structure displayed on Figure 1 manufac- tured on GaAs has been tested. The active area of the diode is of octagonal shape with the diagonal of 350 μm The individual diode samples have been selected according to their reverse bias characteristics. The break voltage of the samples was 40 Volts. The construction of the structure manufactured on GaP is on Figure 2. The individual diode samples have been selected according to their reverse bias characteristics. The break voltage of the samples was