Laser effects on donor states in low-dimensional semiconductor heterostructures

A theoretical study of the effects of intense laser fields on the ground-state binding energies of donor impurities in low-dimensional semiconductor heterostructures is performed. The laser-heterostructure interaction is treated within an extended dressed-atom approach, so that, for a laser tuned far below any resonances, the effects of the laser-semiconductor interaction correspond to a renormalization of the semiconductor energy gap and conduction/valence effective masses. Calculations are performed for donors in $\mathrm{GaAs}\text{−}\left(\mathrm{Ga},\mathrm{Al}\right)\mathrm{As}$ quantum wells, cylindrical quantum-well wires, and spherical quantum dots. The binding energies of donors in low-dimensional systems increase with increasing laser intensity, and for a fixed intensity, the influence of the laser is stronger for small detunings. Results obtained within the extended dressed-atom approach are compared with previous calculations performed by using a simplified high-frequency limit of the Kramers-Henneberger approach.

Figure 1

(a) On-center donor binding energies as functions of the (a) laser intensity for a detuning $\delta =0.05{ϵ}_g$ and (b) laser detuning, with a laser intensity $I=0.5\times {10}^{10}\mathrm{W}∕{\text{cm}}^2$, for ${\text{GaAs-Ga}}_{0.7}{\mathrm{Al}}_{0.3}\mathrm{As}$ QWs with $L=100\mathrm{\AA }$ and $300\mathrm{\AA }$ widths. Results for bulk $\mathrm{GaAs}$ are shown as dotted curves. The upper horizontal axis corresponds to the ${\alpha }_o$ parameter defined in the text.

Figure 2

(a) Donor binding energies as functions of the (a) laser intensity for a detuning $\delta =0.05{ϵ}_g$ and (b) laser detuning, with a laser intensity $I=0.5\times {10}^{10}\mathrm{W}∕{\text{cm}}^2$, for ${\text{GaAs-Ga}}_{0.7}{\mathrm{Al}}_{0.3}\mathrm{As}$ cylindrical QWWs (solid lines, on-axis donors) and spherical QDs (dotted curves, on-center donors) with radii equal to $50\mathrm{\AA }$, $100\mathrm{\AA }$, and $200\mathrm{\AA }$.

Figure 3

On-center donor binding energies as functions of the laser intensity for a laser detuning $\delta =0.05{ϵ}_g$, for ${\text{GaAs-Ga}}_{0.7}{\mathrm{Al}}_{0.3}\mathrm{As}$ (a) QWs with length equal to $100\mathrm{\AA }$ and $300\mathrm{\AA }$, and (b) spherical QDs with radii equal to $100\mathrm{\AA }$ and $200\mathrm{\AA }$. Full curves are results of the present work whereas full symbols and dashed curves are associated to the MHFA calculations (Ref. 6).