Integral and fractional charge filling in a InAs/GaAs quantum dot $p–i–n$ diode by capacitance–voltage measurement

The temperature-dependent capacitance–voltage $(C–V)$ characteristics of two stacked InAs/GaAs quantum dot $p–i–n$ diode were investigated. The capacitance discontinuities observed are attributed to charge storage in the InAs quantum dots. The average storage electrons at each InAs quantum dot thus obtained are two and three electrons at room temperature and at temperature below 100 K, respectively. In the intermediate temperature range from 100 to 250 K, fractional charge occupation is observed in each dot. When the $C–V$ measurement frequency is lowered from 800 to 80 kHz, the capacitance turns into a negative value under low biases which indicates the dominance of the inductance at lower frequency.