1 ML Wetting Layer upon Ga(As)Sb Quantum Dot (QD) Formation on GaAs Substrate Monitored with Reflectance Anisotropy Spectroscopy (RAS)

Abstract

III/V semiconductor quantum dots (QD) are in the focus of optoelectronics research for about 25 years now. Most of the work has been done on InAs QD on GaAs substrate. But, e.g., Ga(As)Sb (antimonide) QD on GaAs substrate/buffer have also gained attention for the last 12 years. There is a scientific dispute on whether there is a wetting layer before antimonide QD formation, as commonly expected for Stransky-Krastanov growth, or not. Usually ex situ photoluminescence (PL) and atomic force microscope (AFM) measurements are performed to resolve similar issues. In this contribution, we show that reflectance anisotropy/difference spectroscopy (RAS/RDS) can be used for the same purpose as an in situ, real-time monitoring technique. It can be employed not only to identify QD growth via a distinct RAS spectrum, but also to get information on the existence of a wetting layer and its thickness. The data suggest that for antimonide QD growth the wetting layer has a thickness of 1 ML (one monolayer) only.

Doped or Quantum-Dot Layers as In Situ Etch-Stop Indicators for III/V Semiconductor Reactive Ion Etching (RIE) Using Reflectance Anisotropy Spectroscopy (RAS)

“…In our material system, QD growth might start with the evolvement of a so-called wetting layer of the QD material, before the QD themselves emerge. Typically, we find wetting layers of 0-1 ML [4]. In all four cases, the RAS signal shows a significant peak, as soon as the wetting layer or the QD layer starts to grow.…”

“…In our material system, QD growth might start with the evolvement of a so-called wetting layer of the QD material, before the QD themselves emerge. Typically, we find wetting layers of 0–1 ML [ 4 ].…”

“…In our material system, QD growth might start with the evolvement of a so-called wetting layer of the QD material, before the QD themselves emerge. Typically, we find wetting layers of 0-1 ML [4]. The sensitivity of RAS with respect to doping impurities allows for the determination of doping concentrations (after calibration runs).…”

“…Most electronic as well as micromechanical devices are based on silicon. Optoelectronic devices, such as semiconductor lasers, often rely on sophisticated sequences of monocrystalline cubic III/V semiconductor layers with heterostructures, intrinsic (i) and doped (n, p) layers, quantum films, and quantum dots (QD) [ 4 , 5 , 6 ]. Depending on the complexity and functionality of the device under consideration, the dry-etch process might have to be terminated at a certain depth with accuracies better than tens of nanometers [ 5 ].…”

“…Reactive ion etching (RIE) is a core technological process of lithographic semiconductor device fabrication, increasing accuracy and reproducibility in comparison to wet etching [1][2][3]. Typically, a small amount of an appropriate reactive gas (for example, Cl 2 or CF 4 ) is mixed with a larger portion of a nonreactive, so-called plasma gas (usually argon) inside a vacuum chamber.…”