Frequency dependence of negative differential capacitance in p-i-n InGaAs photodetector at room temperature

The negative differential capacitance(NDC) of p-i-n InGaAs/InP photodetector has been clearly observed, and the frequency dependence of the NDC is established, which is a small signal mode based on the accumulation and emission of electrons in the potential well at the p-InP/i-InGaAs interface state. The change of energy band was taken into account at the p-InP/i-InGaAs interface with the variation of the bias voltage. The NDC phenomenon is contributed by the additional capacitance (C-D), which is caused by the charging-discharging process in second energy state (E-d2) of the potential well. From this model, it is found that the NDC is more obvious with the decrease of frequency, which is consistent with the conclusion of the experiment. It is proved that the probability of electron capture/escape in the second energy state of the potential well is affected by frequency. When the capture/escape time of the charge in the potential well is shorter than the frequency of the testing signal, the electrons will leave the potential well and produce a surplus of capacitance. The calculated value is consistent with the experimental result obtained.