Optical Properties Of Semiconductor InGaAs/GaAs Surface Quantum Dots

Surface quantum dots(SQDs)have been investigated extensively due to the unique surface sensitive properties and the great potential for developing gas-detector devices.In this research,the optical properties and carrier dynamics of InGaAs/GaAs SQDs have been studied by photoluminescence(PL),photoluminescence excitation spectrum(PLE),and time-resolved photoluminescence(TRPL)technologies,in order to reveal the impact of Fermi level pinning and the intra/inter layer coupling on the optical properties of SQDs.The research includes:At first,the optical properties of single layer of InGaAs SQDs and buried quantum dots(BQDs)have been comparatively studied.The PL of SQDs measured at 10 K indicated that,the peak energy blueshifts while the linewidth(full width at half maximums,FWHM)initially decreases and then increases with increasing the laser intensity.Also,the PL peak energy of SQDs linearly depends on the cube root of the laser intensity.These results suggest that the surface Fermi level pinning cause the separation between electrons and holes,resulting a builtin electric field and a type-II band alignment as well as the type II radiation characteristics for the SQDs.Then,the interplay effect of Fermi level pinning and intra-layer coupling on the fluorescence characteristics is investigated for InGaAs SQDs with different density by manipulating the growth temperature.Under weak laser excitation intensity and low temperature of 10 K,the peak energy of SQDs blueshifts while the FWHM initially decreases and then increases with increasing the laser intensity,no matter the SQDs have intra-layer coupling or not.In composition of two samples grown at 490? and 520?,it is found that the variations of the PL peak energy and FWHM for SQDs are mainly caused by the Fermi level pinning effect and the intra-layer coupling among neighbor dots contribute less.After that,carrier injection into SQDs from a single layer of BQDs or InGaAs QW thorough a 10 nmGaAs spacer is studied via luminescence measurements.The results confirm that such injection structures can provide more carriers for the SQDs.However,the QW injection structure is less efficient than the BQDs injection structure although the QW in general can collection more carriers than single layer of BQDs.This is significant different from traditional carrier injection from QW into BQDs.In addition,both QW and BQDs can provide additional carriers to the SQDs.But the carriers injected from QW or BQDs are much less than the density of surface states.Thus,the carrier injection can not significantly modify the SQDs emission intensity and decay time.The results in this research indicate that the optical properties of SQDs not only depend on the SQD emission,but also being influenced by surface Fermi level pinning,intra/interlayer coupling among SQDs,and carrier dynamics including carrier injection and carrier relaxations.The results obtained in this research will help not only to understand the physical properties of SQDs,but also to develop gas-detector devices by using InGaAs/GaAs SQD.