Strain relief in linearly graded composition buffer layers: A design scheme to grow dislocation-free (<105 cm−2) and unstrained epilayers

Abstract

The strain relaxation in linearly graded composition InGaAs layers grown on (001) GaAs substrates by molecular beam epitaxy is studied by transmission electron microscopy (TEM) and double crystal x-ray diffraction (DCXRD). The dislocation distribution in these layers does not coincide with the predicted equilibrium dislocation distribution [J. Tersoff, Appl. Phys. Lett. 62, 693 (1993)]. The dislocation density in the dislocation-rich layer thickness is slightly smaller than the equilibrium density. The thickness of the dislocation-rich region is different in the [110] and [11̄0] directions. A good correspondence exists between the TEM and DCXRD strain measurements. The dislocation distribution observed by TEM has made it possible to design a scheme to grow dislocation-free and unstrained top layers on linearly graded composition buffer layers.

Low-Temperature and Metamorphic Buffer Layers

“…Buffer layers with linearly-graded composition, and therefore lattice constant, have been extensively investigated in a number of material systems, including In x Ga 1Àx As/GaAs [25,26,51,[96][97][98][99][100][101][102][103][104], In x Al 1Àx As/GaAs [34,75,103,[105][106][107][108][109][110], In x Al y Ga 1ÀxÀy As/GaAs [18,19,23,35,80,95,111], Si 1Àx Ge x /Si [112][113][114][115][116], In x Ga 1Àx P/GaAs [117][118][119], In x Ga 1Àx P/ GaP [120], ZnS y Se 1Ày /GaAs [102,121], and In x Ga 1Àx Sb/GaSb [122,123]. A possible advantage of continuous grading is that layer-by-layer growth may be maintained without the intrusion of island growth associated with large, abrupt changes in composition [119].…”

Investigation of metamorphic InGaAs quantum wells using N-incorporated buffer on GaAs grown by MBE

“…The latter problem is more critical for the optoelectronic devices such as lasers, which have large device areas and therefore are very sensitive to TDs in the active region. Several different metamorphic buffer designs have been implemented to reduce the TD density, e.g., use of a thick uniform buffer layer [4,5], a step-graded buffer layer [6,7] and a continuously graded buffer layer [8][9][10][11]. Other structures like strained superlattice (SL) [12] and quantum dots [13] are also employed to block TDs after they have been generated.…”

Strain relaxation and it’s mechanism of single Si1-xGex/Si epilayer structures grown on Si(00l) substrate

“…After relaxation some residual strain may remain in the epilayer. Several techniques such as X-ray diffraction (XRD) [7], Photolumine~ence (PL) [8], and TEM [911 have been used for the measurement of residual strain.…”