Abstract
A detailed analysis of the electrical response of In0.3Ga0.7As surface quantum dots (SQDs) coupled to 5-layer buried quantum dots (BQDs) is carried out as a function of ethanol and acetone concentration while temperature-dependent photoluminescence (PL) spectra are also analyzed. The coupling structure is grown by solid source molecular beam epitaxy. Carrier transport from BQDs to SQDs is confirmed by the temperature-dependent PL spectra. The importance of the surface states for the sensing application is once more highlighted. The results show that not only the exposure to the target gas but also the illumination affect the electrical response of the coupling sample strongly. In the ethanol atmosphere and under the illumination, the sheet resistance of the coupling structure decays by 50% while it remains nearly constant for the reference structure with only the 5-layer BQDs but not the SQDs. The strong dependence of the electrical response on the gas concentration makes SQDs very suitable for the development of integrated micrometer-sized gas sensor devices.
Highlights
In recent years, the presence of hazardous chemicals, urban environmental pollutants, and dangerous pollutants in food has promoted the development of high-sensitivity sensors and new sensing materials [1,2,3,4]
The reference sample shows a perfect Gaussian PL signal centered at 1188 meV with a linewidth of 53.48 meV, which can be attributed to the fundamental electronic transition in the five layers of buried quantum dots (BQDs) [17]
The surface quantum dots (SQDs) peak is redshifted with respect to that of the BQDs by about 240 meV, because the SQDs are not strained by a capping layer and their lattice constant and the band gap approaches the natural values [15, 17]
Summary
The presence of hazardous chemicals, urban environmental pollutants, and dangerous pollutants in food has promoted the development of high-sensitivity sensors and new sensing materials [1,2,3,4]. Semiconductor nanomaterials are ideal gas sensing materials due to their unique small size effect, surface effect, and quantum effect. Surface quantum dots (SQDs) have attracted much attention in the application field of gas sensing materials [10,11,12]. Optical properties of coupling structure with the SQDs stacking on multilayer buried quantum dots (BQDs) have been studied in depth [13,14,15]. In such coupling structures, carriers transferred from BQDs to SQDs have important influence to enhance photoluminescence (PL) efficiency. The results show that the multi-layer coupled quantum dots structure is very sensitive to the surface
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