WIN Seminar - Professor Itaru Kamiya: "Epitaxial Growth and Characterization of InAs-based Structures on GaAs"

The Waterloo Institute for Nanotechnology (WIN) presents a seminar by Professor Itaru Kamiya, from the Quantum Interface Laboratory, Toyota Technological Institute, Nagoya, Aichi Japan.

Epitaxial Growth and Characterization of InAs-based Structures on GaAs

Abstract

Lattice-mismatch is an unavoidable problem we face when preparing device structures using epitaxial growth. Crystal growth of lattice-mismatched materials leads to nonplanar structures, often leading to three-dimensional (3D) structures. In the growth of InAs on GaAs(001),the fact that growth proceeds in Stranski-Krastanov mode was taken as an advantage for the preparation of quantum dots (QDs).

Despite the lattice mismatch, InAs-based quantum structures have attracted attention due to their potential to be applied to near infrared (NIR) optoelectronic devices. In particular, those tuned to 1.55 μm for telecommunications using InAs quantum dots (QDs) has been both a technological and scientific challenge. InAs QDs are typically prepared epitaxially by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) on GaAs(001) substrate. However, the luminescence from these self-assembled (SA) QDs is usually observed at around 1.0 to 1.2 μm despite the band alignment that makes tuning to 1.55 μm look easy. Not surprisingly, it was revealed that the strain that induced the QD formation also plays a significant role in determining the electronic states. In short, the strain induced in the InAs QDs by the GaAs barrier layers blueshifted the luminescence.

To overcome this problem, we introduced novel structures that control the strain induced in the QD, with which, we have been successful in obtaining photoluminescence (PL) with peak at ~1.62 μm at 4K and ~1.73 μm at room temperature (Fig. 1). This involved modification of the barrier layers to reduce the strain and enhance the PL intensity. We performed detailed analysis of the morphology and lattice constants of both the QDs and cap layers using atomic force microscopy (AFM), and in situ X-ray diffraction (XRD) at SPring-8 beamline 11XU, using a combined MBE-XRD system to reveal the lattice dynamics during MBE growth. The carrier dynamics involved in the PL enhancement will also be addressed.

We further point out that QD is not the only structure obtained by growth of InAs on GaAs(001). We will discuss structure which we call quantum well islands (QWIs) has an advantage over the QDs for photon upconversion [9-11], and also thick films that are grown for tandem solar cells.