Scanning Tunneling Microscopy/Spectroscopy Study of Self-Organized Quantum Dot Structures Formed in GaP/InP Short-Period Superlattices

Abstract

Self-organized quantum dot (QD) structures formed in (GaP) n (InP) m short-period superlattices (SLs) grown on GaAs (N11) substrates by gas source MBE (molecular beam epitaxy) are studied by scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). STM images show high density QD structures as bright areas. The dot size of these structures ranges from 15 nm to 25 nm with a dispersion of ±10% depending on the n and m of the SLs. In the STS measurement, the voltage width for dI/ dV=0 varies along the lateral direction on the sample surface. This voltage width variation corresponds to the lateral variation of the band-gap energy and of the tunneling probability by the lateral composition modulation.

Spectroscopic study of self-organized quantum dot like structures in Ga–In–P superlattices on (311) GaAs

“…Several samples were grown with different GaP/InP layer thickness on differently oriented GaAs substrates. 9,10 From among them, the present study concentrates on the sample which shows maximum anomaly in the temperature dependence of its PL peak position. The sample structure is shown schematically in Fig.…”

“…STM studies on the SPS planes of the sample in Fig.1 show that the Ga/In rich regions form globular structures with a distribution in diameters. 10 The distribution ͑average for ͓011͔ and ͓233͔ directions͒ can be approximated by a Gaussian with a mean diameter of Ӎ 210 Å and a full width at half maximum of Ӎ 50 Å. Since InP has a smaller band gap than GaP, from the point of view of electronic band structure, the In rich globules within the SPS layers represent potential troughs for electrons and holes surrounded on four sides by the Ga rich regions which act as barriers.…”

“…8 Thereafter Kim et al 9 showed that the SILCM process can give rise to QD-like structures when the ͑GaP͒ m ͑InP͒ n SPS are grown on GaAs ͑N11͒ substrates as evidenced from TEM pictures and scanning tunneling microscopy ͑STM͒ studies. 10 It was also reported that some of these samples did not show the expected regular increase in the photoluminescence ͑PL͒ peak energy position with decreasing temperature. 9 There have been several other reports of anomalous temperature dependence of PL peak positions in Ga-In-P based systems some of which have been attributed to ordered alloy formation.…”

Structural and optical characterization of self-formed GaP/InP quantum dots

“…In fact, the (GaP) 2 (InP) 2.5 SLs formed the larger period (~22 mn) of QDs. 10 The difference in the lateral period of dots between (GaP) 1.5 (InP) 1.88 and (InP) 1.88 (GaP) 1.5 is possibly due to the difference of strains of the first layer on the GaAs substrate due to the difference in both lattice constant and monolayer numbers. The highresolution cross sectional TEM of the interface between dot structures and buffer layer would be desirable, but it has not yet been observed.…”

1.3-1.5 μm wavelength quantum dots self-formed in GaAs/InAs superlattices grown on InP (411) substrates

“…Lateral periodic variation of bandgap energy was clearly observed with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) [2]. We have already reported their good optical properties [3] and achieved the current injection laser operation [4]. However, the emission from the above mentioned QDs was in the 0.62-0.67 p m wavelength range.…”