Structural characterization of GaInNAs/GaAs double quantum well structures

Abstract

We performed a structural analysis of strained GaInNAs/GaAs double quantum well samples (about 2% N content) having various well-layer thicknesses and investigated the relaxation process beyond the critical thickness. We used photoluminescence (PL) measurements, x-ray diffraction measurements, and transmission electron microscopy (TEM) analysis. PL measurement reveals deterioration of crystal quality as the well thickness increases. X-ray diffraction reveals that no serious relaxation occurs even when the deterioration proceeds. Cross-sectional and plan-view TEM analysis clarify the deterioration process in detail. In a sample with thin well layers, local dark spots are first generated only at the first well layer, whereas no such dark spots are observed in the second well layer. Through careful observation, the dark spots are identified as local defects (dislocation loop), not the quantum dot structures reported for other materials. For samples with thicker wells, large dark spots penetrating both well layers are observed. Furthermore, threading dislocations and/or stacking faults, which derive from the dark spots, are also observed in the upper GaAs cladding layers. However, no misfit dislocations are observed in any samples, although two-dimensional growth is confirmed. These results indicate a different type of deterioration from that conventionally reported in InGaAs/GaAs material systems. The relationships between the deterioration process and growth process are discussed based on the interface smoothness. The discussion clarifies that dynamical processes play essential roles in the deterioration.

Studies on TlInGaAsN double quantum well structures

“…The HRTEM images of the dark spots observed in the modified barrier samples showed the presence of discontinuity in the lattice planes indicating the existence of extra-planes or defects in the dark spots. Thus, this dark spots may not correspond to quantum dots, applying the analogy of [6]. However, the widely pointed out spinodal decomposition in the GaInNAs system [8] and many reports on the growth or generation of quantum dots in GaInNAs system [9] support the interpretation of dark spot to be quantum dot formation.…”

“…Comparatively, structures with combined barriers showed In addition, at certain interfaces dark spots are also observed. Such an observation of undulation and dark spots has been reported in the case of GaInNAs/GaAs DQW structures [6,7]. Nakashima et al have reported the origination of the threading dislocations and/or stacking faults from the dark spots in the DQW layers [6].…”

X-ray Diffraction Measurement of GaInNAs/GaAs Double Quantum Well Structures with Novel Analysis Method for Broadening Factors

“…Owing to the above preliminary analysis, we can straightforwardly focus on the broadening due to the size effects of the quantum well structures as the probable main broadening factor for sample D. The TEM analysis reported in our previous papers 14,17) revealed that defects are mainly introduced in the first well layer. This implies that the degree of deterioration differs between the first and second well layers.…”

MBE growth and characterization of TlInGaAsN double quantum well structures

“…Thus, the dark spots may not correspond to quantum dots, applying the analogy of Ref. [7]. However, the widely pointed out spinodal decomposition in the GaInNAs system [9] and many reports on the growth or generation of quantum dots in the same system [10] support the interpretation of dark spots as quantum dots formation.…”

“…In addition, at certain interfaces dark spots are also observed. Such an observation of undulation and dark spots has been reported for the case of GaInNAs/GaAs DQW structures [7,8]. Nakashima et al have reported the origination of the threading dislocations and/or stacking faults from the dark spots in the DQW layers [7].…”