Carrier diffusion in InAs/GaAs quantum dot layers and its impact on light emission from etched microstructures

Abstract

We have studied carrier diffusion in self-assembled InAs/GaAs quantum dots (QDs) and light emission from deeply etched microstructures containing QDs using a novel micro-photoluminescence technique based on scanning the laser excitation spot across an etched feature. Complete suppression of carrier diffusion is observed in these QDs at temperatures less than 150 K. At temperatures above 150 K the carrier diffusion length in the QD layer increases with increasing temperature but remains less than the carrier diffusion length in an InGaAs/GaAs quantum well (QW). Carrier diffusion lengths of 6.5 and 9.5 µm were measured for the QD and QW layers at room temperature, respectively. Photoluminescence spectra measured on the same QD sample over the 77–297 K temperature range indicate carrier redistribution occurring between different sized dots in the layer at temperatures above 70 K, suggesting carrier trapping in only the larger dots in the layer is sufficient to prevent carrier diffusion. The expected increase in non-radiative edge recombination in deeply etched microstructures with increasing carrier diffusion length is observed for etched photonic bandgap structures containing both QD and QW active layers. Despite the reduced carrier diffusion length in QD active layers, edge effects dominate carrier recombination processes in a 3.2 µm diameter etched microstructure containing InAs/GaAs QDs at room temperature.

Dual-state lasing and the case against the phonon bottleneck

“…The main difference is in the lateral diffusion length, which is much greater for the QW laser than the QD laser [12]. Lateral diffusion of carriers would be expected to be the dominant mechanism of current re-direction between filaments which is indicated by the resistor bridging the two filaments in figure 1(c).…”

The measured dependence of the lateral ambipolar diffusion length on carrier injection-level in Stranski-Krastanov quantum dot devices

“…4,5 Some have even attempted to compare the lateral ambipolar diffusion length ͑L d ͒ and shown it to be smaller in quantum-dots than quantum wells. [6][7][8] However, the values for L d range considerably ͑0.1-5 m͒ and more significantly there still remains some ambiguity in the mechanism of lateral diffusion in the coupled system of quantum-dots, wetting-layer, and barrier material.…”

“…The range of carrier injection-levels that we perform the analysis on extends to the high injection-level regime where real "working" devices operate. In comparison, the cathodoluminescence 19,20 and photoluminescence 6,21,22 studies are performed under low injection-levels on specifically designed and sometimes unrealistic material structures.…”

A new method for direct extraction of ambipolar diffusion length in a thin film by scanning photoluminescence microscopy

“…T o understand the carrier transport property in a thinfilm structure, there have been several methods of spatially resolved techniques, such as scanning photocurrent microscopy (SPCM), [1][2][3][4][5][6][7][8][9] electron-beam-induced current (EBIC), [10][11][12] cathodoluminescence (CL) or photoluminescence (PL) based measurement, [13][14][15][16][17][18][19][20] and ultrafast measurement. [21][22][23] For materials that are not sufficiently luminescent, such as Si, the diffusion length can be extracted by SPCM, EBIC and ultrafast measurement.…”