Recent advances in the integration of bare silicon die into Multi-Chip Modules (MCM), combined with advanced cooling methods, and innovative circuit design, will be utilized for the development and construction of a high speed (>20MHz), high quantum efficiency (>30%), dynamically linear, low noise, photon counting detector. The results will be achieved by integrating off-the-shelf high performance avalanche photo-diode (APD) silicon die with innovative support circuitry die, to produce a miniaturized high performance APD detector. Special attention will be paid to minimizing thermal resistance by utilizing diamond film substrates and Peltier cooling devices. The Phase I design and development will be achieved in several stages. First, the best support circuit design to increase the photon count rate, reduce dead-time, and increase the quantum efficiency of a state-of-the-art APD in the Geiger counting configuration will be selected. Second, an investigation will be made into facilities to custom manufacture MCMs for the circuit integration and manufacture. The final report will include a final circuit design, a preliminary MCM design, and recommendations for facilities to be used for MCM development and manufacture. Commercial Applications:High performance photon counting applications such as: optical time domain reflectometry (OTDR), optical interferometry, absorption and emission spectroscopy, Raman spectroscopy, densitometry, optical communications, imaging, scintillation counting, Lidar receivers, laser metrology, laser velocimeters, laser altimeters, optical pulse timing, wave-front detection, biological measurements, low-level luminescence measurements, etc.