Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Evaluation of Uni-Traveling Carrier Photodiode Performance at Low Temperatures and Applications to Superconducting Electronics 31 of the customized modules. On the other hand misalignment did not occur for the standard one. The cause of the misalignment was due to the bending of the optical fiber. The problem was finally resolved by shortening the free space of the fiber without ferrule and by uniformly gluing the fiber to the ferrule with epoxy resin as shown in Fig. 5 a . Figure 5 b is a photograph of the entire module which has a coaxial V-connector for a wide-band electrical output and DC terminals. a b Fig. 5. Photographs of customized UTC-PD a UTC-PD chip and fiber lens and b entire module. The equivalent circuit of a negative type UTC-PD module is shown in Fig. 6. In the negative type the UTC-PD module is usually negatively biased to accelerate electron drift in the depletion layer increasing the operating speed. The output signal is inverted to the input signal. A termination resistor of 50 Q for impedance matching is integrated at the output of the chip. 50 Q negative 50 Q -----o Output 2200 pF 200 pF Photodiode chip Fig. 6. Equivalent circuit of negative-type UTC-PD module. DC characteristics at low temperature The current versus voltage I-V characteristics of our customized UTC-PD module was measured at operating temperatures from 4 to 300 K as shown in Fig. 7. No electrical and 32 Photodiodes - Communications Bio-Sensings Measurements and High-Energy Physics mechanical damage was observed from the I-V characteristics in our experiments when the UTC-PD module was cooled using a cryocooler at a cooling rate of around 1 degree minute. Since the gap energy of the InGaAs increased and thermal energy decreased the forward voltage at which the current rapidly increased somewhat increased. The forward voltage increased around V by cooling from 300 K to 4 K. The forward current increased sharply at this forward voltage as the operating temperature .
