Highly uniform and strain-free GaAs quantum dots fabricated by filling of self-assembled nanoholes

Abstract

We demonstrate the self-assembled creation of a novel type of strain-free semiconductor quantum dot (QD) by local droplet etching (LDE) with Al to form nanoholes in AlGaAs or AlAs surfaces and subsequent filling with GaAs. Since the holes are filled with a precisely defined filling level, we achieve ultrauniform LDE QD ensembles with extremely narrow photoluminescence (PL) linewidth of less than 10 meV. The PL peaks agree with a slightly anisotropic parabolic potential. Small QDs reveal indications for transitions between electron and hole states with different quantization numbers. For large QDs, a very small fine-structure splitting is observed.

Single-dot Spectroscopy of GaAs Quantum Dots Fabricated by Filling of Self-assembled Nanoholes

“…We present results of two type I samples, one with n P = 3 and one with n P = 7, which corresponds to GaAs layers with thickness d f = 0.34 nm and 0.79 nm, respectively. The additional type II sample was filled with d f = 0.57 nm resulting in uniform QDs with height of 7.6 nm [25]. Finally, the QDs were capped by a 120-nm-thick Al 0.35 Ga 0.65 As barrier.…”

Holed nanostructures formed by aluminum droplets on a GaAs substrate

“…The holed nanostructures, first demonstrated by Wang et al [21], are particularly promising candidates for the formation of uniform and low-density quantum rings [22][23][24]. However, all the previously published work has involved the formation of nanostructures from gallium (Ga) or indium (In) droplets [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], and there has been no report of aluminum (Al) droplets on GaAs substrates, although there have been a few of papers involving Al droplets [11,25]. Investigation of the nanostructures formed from Al droplets will not only enrich our knowledge of group Ⅲ droplet epitaxy and facilitate an understanding of provide a solid understanding of such a simple and novel molecular beam epitaxy (MBE) growth process [26].…”

“…2(d). In this diagram, we assume the initial Al droplet has the same behavior as a gallium or indium droplet in that the initial sizes and shapes of the holed nanostructures directly correspond to the initial sizes of the droplets [11,21,22,25] with the following results: (1) the inner ring diameter is the same magnitude as the diameter of the initial droplet; (2) the central hole depth is the same magnitude as the height of the initial droplet; (3) the inner ring height is ~6 nm while the outer ring height is reduced to half this value; (4) the distance between the inner and outer rings is 200 nm ± 20 nm. It should be noted that the large flat spacing between Al concentric double rings observed in this work is one distinguishing feature from the ordinary compact concentric double rings or multiple concentric nanorings observed for Ga droplet epitaxy [17].…”

Thermally controlled widening of droplet etched nanoholes

“…For example, this allows the creation of strain-free GaAs quantum dots [14-16] with the capability to precisely adjust the dot size by filling the holes only partially. Furthermore, the realization of ultra-short nanopillars [17] has been demonstrated.…”