The use of graded InGaAs layers and patterned substrates to remove threading dislocations from GaAs on Si

Abstract

We have investigated threading dislocation (I'D) removal from GaAs films on Si by introduction of additional InGaAs graded strain layers in combination with growth on patterned substrates. The substrate patterns consisted of mesas with lo-34 ,wm widths. The mesa sidewalls were either overhanging (concave), leading to free sidewalls for the film on the mesas, or outward sloping (convex) sidewalls with (111) orientation. The dislocation structure was studied using transmission electron microscopy. It was found that the graded strained layers led to a reduction of dislocation density by a factor of -5 in films grown both on mesas with concave sidewalls and on unpatterned substrates. This reduction was due to dislocation reactions leading to annihilation of TDs. For films with graded strained layers on mesas with convex sidewalls, an additional factor of -3 reduction in TD density was observed in the part of the tilm that was grown on top of the mesas. In this case all mobile TDs (TDs associated with 60" misfit dislocations, i.e., TDs that could glide to relieve misfit stress) were removed from the film on top of the mesas to the regions above the sidewalls and only TDs associated with'90" misfit dislocations remained. We suggest that this is due to pinning of the TDs associated with 60" misfit dislocations at the mesa edges and we have presented an explanation for this pinning in terms of the stress conditions at the (111) oriented mesa edges. In addition, this leads us to suggest that in order to obtain minimum TD density it is imperative to prevent formation of 90" misfit dislocation during lattice mismatched heteroepitaxial growth.

AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique

“…From the RSM data shown in Fig. In addition, the previous report indicated that the strain in the epi-layer can exerted a net force on the dislocation, and the dislocation could be bent and terminated at an epilayer edge, without threading through the epilayer to the top surface of the epi-layer [15]. In addition, the reciprocal lattice points of AlGaN and GaN were lined up at the same Q x position, i.e.…”

Threading Dislocations in InGaAs CaP Layers with InGaAs Graded Layers Grown on Si Substrates

“…However, the TD density described above is high for device applications. The reported TD density of the previously mentioned GaAs layer on the Si substrate 6) was 7 Â 10 8 cm À2 , which is a typical value for as-grown layers using two-step growth. 7) The TD density of an InGaAs layer on a Si substrate might decrease if the TD density of a GaAs layer on a Si substrate is lowered using the reported methods such as thermal cyclic annealing (TCA) or a strained superlattice.…”

“…5) Reduction of the TD density to the order of 10 7 cm À2 was achieved in InGaAs layers on GaAscovered Si substrates with graded buffer layers using molecular beam epitaxy. 6) This achievement suggests that InGaAs layers with low TD densities can be grown on high-quality GaAs layers on Si substrates. Furthermore, the graded layer is attractive because it allows the variation of the In composition of the InGaAs layer to a desired value.…”

Low-Temperature and Metamorphic Buffer Layers

“…Step-graded buffers have been investigated in a number of material systems including In x Ga 1Àx As [27,28,[66][67][68][69], In x Al 1Àx As [24,39,68,[70][71][72][73][74][75][76][77][78][79][80], In x Al y Ga 1ÀxÀy As [19,35,80], and Al x Ga 1Àx Sb y As 1Ày [52,81] on GaAs (001) substrates, InAs y P 1Ày [29,[82][83][84] on InP (001), and In x Al 1Àx Sb [85] on GaSb (001).…”