Modeling of dark current in midinfrared quantum well infrared photodetectors

We present a model for the description of dark $IV$ curves in midinfrared quantum well infrared photodetectors at low temperatures, in a regime where dark current is dominated by interwell tunneling. The model separates the $IV$ curve into a low-field and a high-field region allowing us to identify the effects ascribed to miniband transport and carrier localization, respectively. At low fields the system is thought as a superlattice and described by means of a high-density correction of the Esaki-Tsu model. This approach allows us to simulate current saturation phenomena that occur at low temperatures at intermediate fields. On the other hand, high-field transport effects are described in the localized Wannier-Stark basis in order to account for tunneling and field-assisted thermionic emission effects. We then compare simulations with our measurements of the $IV$ curves of mid-IR quantum well infrared photodetectors finding good quantitative agreement between theory and experiment.

Figure 1

(Color online) Current voltage characteristics of the device at different temperatures. The current shows no dependence on temperature up to 20 K, and then its roughly exponential increase denotes the onset of the thermionic regime.

Figure 2

Conduction band profile and normalized wave functions for the QWIP under study. The gray shaded regions represent the miniband along the growth direction.

Figure 3

Low field $IV$ curve computed by the high-density Esaki-Tsu mode for $\tau =100\text{fs}$ (dash-dot line), $\tau =50\text{fs}$ (dashed line) and $\tau =20\text{fs}$ (continuous line). Circles show experimental data at 10 K.

Figure 4

Transmission coefficient of 1, 2, and 3 superlattice periods as a function of electric field. When the electric field is high enough that the electrons can escape into the continuum through one trapezoidal value the three curves almost coincide but at low fields the presence of an additional barrier strongly reduces the transmission.

Figure 5

(Color online) Comparison between computed $IV$ curves (lines) and experimental data (dots) at temperatures of 10 (black), 40 (blue), 50 (green), and 60 K (red).

Figure 6

Computed (squares) and measured (circles) saturation current for three additional devices with 26% Al concentration, 5 nm well and varying barrier width of 15, 20, and 25 nm.

Figure 7

(Color online) Separated view of all the current components used to compute the IV curves in Fig. 5 at 20 K. The dominant contributions are the ground miniband current at low fields and the groun-to continuum tunneling current at high bias.

Figure 8

(Color online) Separated view of all the current components used to compute the $IV$ curves in Fig. 5 at 50 K. Current coming from electrons tunneling from the first-excited state into the continuum is clearly dominant over the whole bias range.