Subthreshold diode characteristics of InAs/GaAs quantum dot lasers

The temperature dependence of the carrier dynamics in ensembles of InAs/GaAs quantum dots (QDs) are of interest, both from a fundamental point of view but also because of the consequences for the performance of QD-based optoelectronic devices. While this topic has been studied before using optical techniques, here we approach the topic by analyzing the current-voltage (I-V) characteristic of QD diodes. Using a current-modulation technique, the transition from “traplike” to “thermalized” behavior as the temperature is raised from 80 K to room temperature is observed. Furthermore, the results suggest that the I-V curve is sensitive to the separate escape of electrons and holes, and the intersubband spacing of the electron states and that of the hole states is estimated from the data.

Figure 1

Electroluminescence spectrum of the QD bilayer laser below threshold at room temperature. The GS emission peak is at 1341 nm and the X1 emission peak is at 1259 nm; the GS and X1 emissions are separated by 60.3 ± 0.3 meV.

Figure 2

An example I-V curve and $-I^2{d}^{2}V/{\mathit{dI}}^2$ spectrum of the QD laser diode. While the latter is different from the expected form of an ideal diode (e.g., the Schottky diode shown for comparison), there is still a clear intercept voltage from which the ideality can be deduced.

Figure 3

(a) The temperature dependence of the switch-on voltage. At low temperatures it is close to the GaAs band gap potential, while near room temperature it is associated with the QD GS energy. (b) The temperature dependence of the ideality factor, extracted from the current modulation measurement. The ideality factor is high at low temperature, peaking near 150 K before dropping toward unity at high temperatures.

Figure 4

$I_S$ calculated from $V_{\mathrm{on}}$ and η. It is suppressed below 150 K because of the efficient capture of carriers into the nonthermal QD states, while at higher temperatures it is thermalized. Inset: Arrhenius plot of the estimated rate-determining barrier energy ${\varphi }_{\mathrm{barrier}}$ together with fit lines as described in the text.