Dark current analysis in InAs quantum-dot APDs with different mesa structures

We investigated the changes in the dark currents in InAs quantum-dot (QD) avalanche photodiodes (APDs) with different shapes of mesas. The APDs were fabricated by using inductively coupled plasma/reactive ion etching (ICP/RIE) or H₃PO₄ chemical etching. The dark currents (I _dark) were observed to be 27 pA for the H₃PO ₄-treated APD and 10 pA for the ICP/RIE-treated APD at -11 V at room temperature (RT). Then, to identify the effect of the mesas on the I _dark of APDs, we measured the temperature-dependent (TD) I-V and C-V characteristics. As a result, we found that at temperatures below 200 K, the TD I_dark of the H₃PO₄-treated APD was still 3 times larger than that of the ICP/RIE-treated APD, while the change of capacitance (ΔC) was 1.09 nF for the H₃PO₄-treated APD and 0.63 nF for the ICP/RIE-treated APD at voltages from 0 V to -12 V. These results indicate that the I_dark of the APDs may be strongly affected by mesas and by the surface conditions of the device and that bulk tunneling and surface leakage shunt currents due to strong electric fields may be the dominant components that determine theI_dark of the H ₃PO₄-treated APD.