The noise characteristics associated with dark current, photoconductive gain (PC), capture probability in doped InAs dots embedded in In<sub>0.1</sub>Ga<sub>0.9</sub>As/GaAs spacer layer have been proposed. The photoconductive and photovoltaic behaviors of the InAs/GaAs quantum dot infrared photodetector (QDIP) from the intersubband transition measurements are also clearly observed. Through noise measurement in dynamic signal analyzer (HP35670A)<sup> 1</sup>, the electronic bandpass filter frequencies are set up ranging from 3 to 10 KHz in a low noise current preamplifier (SR570) <sup>2</sup>. The lock-in amplifier (SR830) <sup>3</sup> can be also used to measure and calibrate the noise density by means of the mean average deviation (MAD) contrast with noise spectra from HP35670A. The InAs/GaAs QDIP studied in this work belongs to n<sup>+</sup>-n-n<sup>+</sup> structure with the top and free blocking barrier layers. It is observed that the owing blocking layer of QDIP not only suppress dark
current successfully but also probably reduce the photocurrent <sup>4-6</sup>. By systematically optoelectronic measurements and simulations, the modified model of noise current, photoconductive gain, and capture probability in the quantum devices have been proposed. It is shown that photoconductive gain is almost independent of bias under the lower bias, then increasing exponentially under higher bias and below the temperature of 80K. In contrast to quantum well infrared photodetector (QWIP), a higher photoconductive gain of the quantum dot infrared photodetector has been demonstrated and attributed to the longer lifetimes of excited carriers in quantum dots <sup>7-10</sup>. At 80K, a photoconductive gain of tens of thousand is shown in the regions of higher biases. It is clear to note that the highest detectivity of the QDIP surprisingly approach to 3.0×10<sup>12</sup> cmHz<sup>1/2</sup>/W at -0.6V under measured temperature 20 K. Under 80K, the average D* is obtained ~10<sup>10</sup> cmHz<sup>1/2</sup>/W. To our knowledge, this is the one of highest D* data in the world.