Characterization of the morphology and optical properties of InAs∕AlAs quantum dots with a GaAs insertion layer

Abstract

InAs self-assembled quantum dots by utilizing a thin GaAs insertion layer (IL) on a 1nm thick AlAs seed layer were grown on GaAs(100) substrates by using a molecular beam epitaxy technique. InAs quantum dots (QDs) were formed by varying the thickness of the GaAs IL from 1 to 9 ML (monolayer), and their morphological and optical properties were characterized by atomic force microscopy and photoluminescence (PL). As a result, when the GaAs IL was thicker than 5 ML, normal InAs QDs with an average diameter of 30nm and a density of 2×1010∕cm2 were formed, because the enhanced surface roughness due to the AlAs layer was leveled by the GaAs IL. However, when the thickness of the GaAs IL was decreased from 5 to 3 ML, the formed InAs QDs showed a bimodal size distribution, i.e., large dots with a lateral size of about 30nm and small dots with that of about 20nm. When the GaAs IL was below 1 ML, InAs QDs with an average diameter of less than 15nm and a high density of 1.5×1011∕cm2 were grown. Consequently, it was verified that the thickness parameter of the GaAs IL had an effect on the size distribution of InAs QDs. Furthermore, although the AlAs layer was used for the purpose of improving the density of the QDs, their PL intensity was comparable to that of the normal InAs QDs.

Comparative analysis of dark current between SiNxand polyimide surface passivation of an avalanche photodiode based on GaAs

“…The epitaxial layers were grown on a (1 0 0) semi-insulating GaAs substrate using MBE. Details of MBE growth and device fabrication were reported in [20,21]. A cross-sectional view of the device is shown in figure 1.…”

“…On the other hand, for GaAsbased PDs, the comparative study between passivation types has been hardly presented for the qualitative and quantitative characteristics of the reverse dark current owing to its limitation of demands and usefulness. However, its performance has become more important in recent years because PD/LED or PD/VCSEL monolithic devices based on GaAs have attracted great interest because of the various optical communicative applications, for example free-space optical interconnect, smart pixel and bio-medical analysis system [16][17][18][19][20][21][22][23][24]. Especially, as these monolithic devices become a one-dimensional or two-dimensional array and their pixel numbers are increased, the research for the surface passivation/leakage current becomes more important because the etched surface is exposed with a larger area and further acts as a dominant noise source.…”

“…Especially, as these monolithic devices become a one-dimensional or two-dimensional array and their pixel numbers are increased, the research for the surface passivation/leakage current becomes more important because the etched surface is exposed with a larger area and further acts as a dominant noise source. We have already reported a polyimide passivation effect, compared with an unpassivated one, and the photocurrent properties with high gain and a dependence of A-M edge profiles of InAs QDs/GaAs separate absorption, charge and multiplication avalanche photodiode (SACM APD) [20,21]. In this paper, we will concentrically present the effect of different surface passivations on the surface dark current and analyze their properties in calculating the theoretical current components.…”

Analysis of surface dark current dependent upon surface passivation in APD based on GaAs

“…The epitaxial layers were grown on a (1 0 0) semi-insulating GaAs substrate using MBE. Details of MBE growth and fabrication are similar to those discussed in [16,17]. The devices contain the SACM APD structure between bottom mirrors and passivation layers.…”

“…To examine the passivation effect, we applied the different passivation processes, one of which is polyimide and the other is SiN x , into the InAs QDs/GaAs SACM APDs. These devices could be used as PDs with low noise, high speed and high wavelength selectivity, and monolithically integrated with VCSELs or LEDs at a wavelength of ∼1 μm [15][16][17]. In this paper, we focus on the passivation effect on surface current.…”