Strain effects and crystal structures of the In xGa 1− xAs active layer in the highly lattice-mismatched In xGa 1− xAs/InP modulation-doped coupled double quantum wells

Abstract

Strain effects in highly lattice-mismatched In x Ga 1− x As/Inp modulation-doped coupled double quantum wells were investigated by transmission electron microscopy (TEM) measurements. The high-resolution TEM images showed that the In 0.53Ga 0.47As/In 0.25Ga 0.75As, In 0.25Ga 0.75As/InAs, and InAs/InP heterointerfaces had very sharp interfacial abruptness. The selected-area electron diffraction pattern obtained from the TEM measurements on the In x Ga 1− x As/InP double quantum wells showed that the In x Ga 1− x As active layers were grown pseudomorphologically on the InP buffer layer in spite of high lattice mismatch among the active layers. Shubnikov–de Haas and Van der Pauw Hall-effect measurements at 1.5 K showed that the mobility of the two-dimensional electron gas existed in the In x Ga 1− x As quantum well was relatively high regardless of the existence of the strain between the In x Ga 1− x As active layers and the InP potential barriers. The values of the horizontal and the vertical strains of the In 0.25Ga 0.75As layer are 1.9845×10 −2 and −1.858×10 −2 Nm −2, respectively, and those of the InAs layer are −3.128×10 −2 and 3.3995×10 −2 Nm −2, respectively. A possible crystal structure for the In x Ga 1− x As/InP double quantum well is presented based on the TEM results. These results can help improve the understanding of the structural properties for potential applications of strained In x Ga 1− x As/InP modulation-doped coupled double quantum wells in long-wavelength optoelectronic devices.