Effect of Non-Square Potential Profile on Electron Transport Lifetime in Al_xGa_1-xAs-Based Double Quantum Well Structures

The electron transport lifetime τ in low-dimensional semiconductor devices based on quantum well structures is an important parameter that decides the transport as well as optical properties. In recent times, the utilization of non-square quantum well structures has boosted the optoelectronic device performance. This chapter reports the variation of τ with the applied electric field Fapp in Alx Ga1-x As-based modulation doped double quantum well (DQW) structures by considering non-square potential profiles such as parabolic (P), V-shaped (V), semi-parabolic (SP), and semi-V-shaped (SV). Here, τ is analyzed by adopting ionized impurity (imp) and alloy disorder (al) scatterings. In the case of DPQW and DVQW systems, two subbands are occupied from Fapp = 0 up to |Fapp| = 5.6 kV/cm. After that, only one subband is occupied. On the other hand, in the case of DSPQW and DSVQW, there occurs the occupation of only a single lowest subband energy level for all Fapp. It is significant to note that the effect of the scattering mechanism on the subband transport lifetime differs by changing the structure potential. For example, when both lower and upper subbands are filled, in the case of DPQW, the imp-scattering decides τ, whereas, in the case of DVQW, both impand al-scatterings equally contribute. The results of τ in the structures given below are compared with the conventional double square quantum well (DSQW) structure and show that τ (DPQW) > τ (DVQW) > τ (DSQW) at Fapp = 0. The results of τ in nonsquare DQW structures will be very helpful in understanding the intricacies of the electro-optical properties of emerging low-dimensional semiconductor devices.

Keywords: Double quantum well structure, Non-square quantum well structures, Transport lifetime.