In situ synchrotron X-ray diffraction study on epitaxial-growth dynamics of III–V semiconductors

Abstract

The application of in situ synchrotron X-ray diffraction (XRD) to the molecular-beam epitaxial (MBE) growth of III-V semiconductors is overviewed along with backgrounds of the diffraction theory and instrumentation. X-rays are sensitive not only to the surface of growing films but also to buried interfacial structures because of their large penetration depth. Moreover, a spatial coherence length up to µm order makes X-rays widely applicable to the characterization of low-dimensional structures, such as quantum dots and wires. In situ XRD studies during growth were performed using an X-ray diffractometer, which was combined with an MBE chamber. X-ray reciprocal space mapping at a speed matching a typical growth rate was achieved using intense X-rays available from a synchrotron light source and an area detector. The importance of measuring the three-dimensional distribution of XRD intensity in a reciprocal space map is demonstrated for the MBE growth of two-, one-, and zero-dimensional structures. A large amount of information about the growth process of two-dimensional InGaAs/GaAs(001) epitaxial films has been provided by three-dimensional X-ray reciprocal mappings, including the anisotropic strain relaxation, the compositional inhomogeneity, and the evolution of surface and interfacial roughness. For one-dimensional GaAs nanowires grown in a Au-catalyzed vapor-liquid-solid mode, the relationship between the diameter of the nanowires and the formation of polytypes has been suggested on the basis of in situ XRD measurements. In situ three-dimensional X-ray reciprocal space mapping is also shown to be useful for determining the lateral and vertical sizes of self-assembled InAs/GaAs(001) quantum dots as well as their internal strain distributions during growth.

Impact of the Shadowing Effect on the Crystal Structure of Patterned Self-Catalyzed GaAs Nanowires

“…The X-ray spot-size provided by the focusing setup is small enough to illuminate NWs of one individual array only while being large enough to average over a meaningful number of NWs in the respective array, which is particularly important for the statistical significance of our results. In addition to ex situ XRD, time-resolved in situ XRD is a non-destructive way of structure characterization during NW growth, ,− from which we can infer information on the evolution of crystal structure of the NW arrays at the various pitches p during growth, as will be shown later.…”

Progress in surface X-ray crystallography and the phase problem

“…105,106) SXRD has also been applied to in situ studies on crystal growth dynamics of III-V semiconductors grown by molecular beam epitaxy that detected not only surface structures of the growing films but also buried interfacial structures because of the large penetration depth of X-rays. 107) Regarding accelerator-based sources, average brilliances are to be saturated as an electron-beam emittance approaches the limitations set by the wavelength of light (diffraction limit), 5) as shown in Fig. 1.…”

In Situ Synchrotron X-ray Diffraction Reciprocal Space Mapping Measurements in the RF-MBE Growth of GaInN on GaN and InN

“…In situ XRD RSM measurements were performed using the MBE apparatus directly coupled to an X-ray diffractometer (Kohzu Precision Co., Ltd., Kawasaki, Japan) at beamline BL11XU of the synchrotron radiation facility SPring-8 (Hyogo, Japan) [26][27][28]. GaInN films were grown on GaN and InN.…”