Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step

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).…”

“…The deposition of each successive step gives rise to lattice relaxation of the underlying layers [75] to maintain the inverse relationship between average strain and thickness. In order to avoid new misfit dislocations in the device layer, the buffer can be designed with compositional overshoot so that the relaxed device layer matches the in-plane lattice constant of the buffer layer [75,76,78,86]. For example, in a step-graded InAs y P 1Ày structure grown on InP (001) by MOVPE for the realization of a mid-IR laser diode, Kirch et al [86] found that the top layer (500 nm InAs 0.68 P 0.32 ) was 90% relaxed and, therefore, contained 10% of the coherency strain.…”

“…In most cases, the dynamical simulations are made necessary by the lack of a one-to-one correspondence between X-ray diffraction peaks and lattice constants present in the sample [87]. Analysis of the X-ray rocking curve, after canceling out the effect of crystallographic tilting by use of the rocking curves measured at opposing azimuths, revealed that the top (device) layer was 98% relaxed using this overshoot design [78]. This is the case for the HRXRC of Figure 25.2, measured from an overshoot step-graded In x Al 1Àx As structure 25 As layer was grown on top of the step-graded buffer.…”

“…Jeong et al made similar observations with step-graded In x Al 1Àx As on GaAs (001). Heyn et al [74] used this same step-graded structure with the inserted strained-layer superlattice to fabricate a shallowchannel InAs HEMT, with the channel 16.5 nm below the surface and exhibiting 4 K channel mobility under illumination of m n ¼ 160,000 cm 2 V À1 s À1 with n s ¼ 6.3 Â 10 11 cm À2 at 4.2 K. [78]. They attributed this effect to alloy hardening, which results in maximum hardness in the middle of the compositional range.…”

“…A 004 high-resolution X-ray diffraction (HRXRD) rocking curve for 1 mm In 0.75 Al 0.25 As grown on a stepgraded In x Al 1Àx As buffer layer with an indium compositional overshoot of Dx os ¼ 0.1[78]. Reprinted from Jiang Z. et al Appl.…”