Near-field second-harmonic generation of semiconductor quantum dots

Liu, AS Bryant, GW

As. Liu et Gw. Bryant, Near-field second-harmonic generation of semiconductor quantum dots, PHYS REV B, 59(3), 1999, pp. 2245-2253

32

INGLESE

Article

Apllied Physucs/Condensed Matter/Materiales Science

PHYSICAL REVIEW B-CONDENSED MATTER

0163-1829 → ACNP

59

3

1999

2245 - 2253

ISI

0163-1829(19990115)59:3<2245:NSGOSQ>2.0.ZU;2-7

Optical second-harmonic (SH) response of a semiconductor quantum dot (QD) e xcited by the near field of a tip in a near-field scanning-optical microsco pe is investigated theoretically. Using an anisotropic effective mass appro ximation, we analyze the frequency- and space-dependent SH nonlinear curren t density in the midgap frequency region associated with interband and inte rsubband transitions in the QD system. Both heavy- and light-hole states co ntribute to the SH signal of the QD system. Assuming that an external field drives the tip and the tip field excites the QD, and neglecting local-fiel d effects, we define an effective SH susceptibility tensor of the QD/tip sy stem in terms of the incident-external field. The second-harmonic generatio n is allowed because the rapidly varying tip field excites the selection-ru le breaking transitions in the QD system. For a given size of the metal-coa ted tip, we performed numerical calculations of the SH susceptibility by sc anning the tip and varying the frequency. We show that the SH nonlinearity of the QD/tip system is strongly dependent on the tip position because the overlap integral of the QD envelope wave functions and the tip field is var ied by scanning the tip over the QD. Our results also show that the spatial distribution of the tip field is reflected in the tip-position dependence of the SH signal. [S0163-1829(99)07103-9].