With the rapid development of technologies for the fabrication of, as well as applications of low-dimensional structures, the demands on characterization techniques increase. Spatial resolution is especially crucial, where techniques for probing the properties of very small volumes, in the extreme case quantum structures, are essential. In this article we review the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission. These techniques are sensitive enough to reveal the electronic structure of low-dimensional semiconductor structures and are, therefore, able to give detailed information about the geometrical structure, including fabrication-related inhomogeneities within an ensemble of structures. The local luminescence probe techniques discussed in this review article can be divided into four categories according to the excitation source: (i) spatially localized microphotoluminescence spectroscopy using either strong focusing or masking; (ii) near-field optical microscopy to reach below the diffraction limitation of far-field optics, by either exciting, detecting, or both exciting and detecting in the near field; (iii) cathodoluminescence using focused energetic electrons in an electron microscope; and (iv) scanning tunneling luminescence, using low-energy electrons injected or extracted from the tip of a scanning tunneling microscope.

Local probe techniques for luminescence studies of low-dimensional semiconductor structures

High quality quantum wells of GaAs confined by barriers of InGaP have been grown by gas‐source molecular beam epitaxy. High‐resolution lattice images obtained with transmission electron microscopy of single quantum wells reveal high quality interfaces for both the normal InGaP/GaAs and the inverted GaAs/InGaP interface. Multiple‐line low‐temperature photoluminescence emission is observed for the thinnest GaAs quantum well. The range of well thicknesses examined was 0.6–5.2 nm, with the smallest well producing a quantum confinement energy shift of over 410 meV, corresponding to photoluminescence emission at 640 nm (1.94 eV) from GaAs.

High quality quantum wells of InGaP/GaAs grown by molecular beam epitaxy

Excitonic relaxation processes in quantum well structures

High quality, GaInAs, single quantum wells lattice matched to InP barriers, have been grown by metalorganic vapor phase epitaxy at reduced pressures and with the application of short growth interruptions at both heterointerfaces. The occurrence of multiple peaks in the 25 K cathodoluminescence spectrum of a sample containing nominally two single quantum wells is caused by terraces differing by one monolayer in thickness, ≊ 2.93 A, in the same quantum well. For their observation as well defined excitonic emission peaks, the terraces must be larger in lateral extent than the free exciton Bohr diameter, namely, ≊ 350 A. This number sets the lower boundary of the size of the terraces. Cathodoluminescence images were formed for the individual emission peaks and the contrast fluctuations observed with a lateral extent up to ≊ 2 μm give the upper boundary for the extended monolayer‐flat terraces. So far this is the first direct observation of such large growth islands at the heterointerface of the GaInAs/InP system.

Cathodoluminescence observation of extended monolayer‐flat terraces at the heterointerface of GaInAs/InP single quantum wells grown by metalorganic vapor phase epitaxy

Influence of growth interruption on the heterointerface morphology ofInGaAsGaAs strained quantum wells

Extended monolayer flat islands occurring at the heterointerface of metalorganic vapor phase epitaxy grown, growth interrupted Al0.5Ga0.5 As‐GaAs single quantum wells are directly observed for the first time by spatially resolved cathodoluminescence (CL). CL images of growth islands with a lateral size of between 500 nm and 2 μm are shown. The photoluminescence emission peak shows splitting corresponding to exciton transitions in the growth islands of the quantum well with a difference in the well thickness of one atomic layer.

M. Mizuta

Papers

Direct observation of extended monolayer flat islands at metalorganic vapor phase epitaxy grown Al0.5Ga0.5As‐GaAs single quantum well interfaces