High lateral density and well-aligned quantum dot (QD) structures are self-formed by growing the (GaP)1.5(InP)1.88 short period superlattices (SLs) on GaAs (311) A substrates. Growth sequence dependence of the QD structures is studied with scanning tunneling spectroscopy and time-resolved photoluminescence spectroscopy. The self-formed dot size for the GaP/InP SLs (GaP is the first growth) is smaller than that for the InP/GaP SLs (InP is the first growth). This difference is considered to be caused by the difference in the strain between the first layer and the substrate. Photoluminescence decay time for the QDs self-formed in the GaP/InP SLs is a little bit shorter than that in the InP/GaP SLs, which is explained by the enhancement of carrier localization due to the increase in overlapping of wave function.

(GaAs)2(InAs)2 short-period superlattices (SLs) were grown on InP (411)A substrates by gas-source molecular-beam epitaxy. Scanning tunneling microscopy observations revealed that the lateral-composition-modulated quantum dot structures were self-formed. They were aligned periodically along two perpendicular lateral directions with a lateral density of approximately 1011 cm-2. Multilayer quantum dot structures sandwiched between InP barrier layers showed strong photoluminescence emission with wavelengths of 1.3–1.6 µm depending on the SL period.

By growing (GaP) 1.5 (InP) 1.88 and (InP) 1.88 (GaP) 1.5 short-period superlattices (the former material is the first layer on the GaAs (311) substrate) by gas source MBE, composition-modulated quantum dots were self-formed in both cases. The dot size is about 20 nm in GaP/InP and 22 nm in InP/GaP sample. The photoluminescence energy is higher for the GaP/InP sample, corresponding to the difference in the dot size. The photoluminescence decay time of the InP/GaP sample is less dependent on the emission wavelength and temperature than that of the GaP/InP sample.

Multilayer quantum dots (MQDs) structures are fabricated on a GaAs(311)A substrate by sandwiching the quantum dots (QDs) self-formed in (GaP)1.5(InP)1.88 short-period superlattices (SLs) with InGaP/InAlP SL layers instead of InGaP layers, as barrier and cladding layers. Narrower photoluminescence (PL) and electroluminescence (EL) linewidths and weaker temperature variations are observed for the modified MQDs compared with the previously reported best values for MQDs with InGaP barrier and cladding layers. PL and EL peak energies for the modified MQDs are higher than those for the previous MQDs. These results suggest the enhancement of carrier confinement by the use of InGaP/InAlP SL layers as barrier and cladding layers. The temperature dependence of EL intensity is also improved.

Growth temperature dependence of the self-formation process of quantum dot (QD) structures in (GaP)1.5 (InP)1.88 short-period superlattices (SLs) grown on GaAs (311)A substrates is studied by scanning tunneling microscopy (STM). SLs are grown by gas-source molecular beam epitaxy (MBE) at 420–500°C. The STM image of the sample grown at 460°C reveals completely self-formed QD structures aligned along both [233] and [011] directions due to the strain-induced lateral composition modulation. On the other hand, both below (420°C) and above (480°C, 500°C) this temperature the self-formation process of QD structures is suppressed and only incomplete structures elongated along the [011] direction are formed, probably due to the suppressed or over-enhanced migration of group III atoms on the surface, respectively. Scanning tunneling spectroscopy (STS) measurements reveal that the amplitude of the lateral periodic variation of the band-gap energy in the self-formed structures also decreases both below and above the optimum growth temperature.

High lateral density and well-aligned In-Ga-P quantum dots on GaAs(N11)A substrate were observed by STM/STS. The superlattice cycle and gas source MBE growth temperature dependence of the self-formed structures were studied by STM. The self-formation process and mechanism were discussed based on these results. The optimum growth temperature exists at around 460°C under the present growth conditions

The nature of emission in quantum dot (QD) structures self-formed in GaP/InP short-period superlattice is investigated in detail by means of time-resolved photoluminescence (TRPL) spectroscopy. PL decay time strongly depends on emission energy and temperature, and ranges from 0.1 ns to 2.5 ns, which can be explained by considering the tunneling effect of carriers and the nonideal dimensionality of dots. The multilayer QD structures with thicker QD layers show a longer PL decay time of up to 1 µs at low excitation densities, which is considered to be caused by an internal piezoelectric field.