Bonding of Elastically Strain-Relaxed GaAs/InGaAs/GaAs Heterostructures to GaAs(001)

Abstract

Bonding of elastically strain-relaxed GaAs/InGaAs/GaAs heterostructures has been achieved on GaAs(001) substrates by the method of in-place bonding. Pseudomorphic heterostructures were patterned and a sacrificial AlAs layer was removed by selective etching. As etching proceeds and the GaAs/InGaAs/GaAs structure is released from the substrate, elastic strain relaxation occurs and the strain-relaxed structures are weakly bonded in-place to the substrate. The bond between the strain-relaxed structure and the substrate was then strengthened by annealing under conditions similar to those used for whole wafer bonding of GaAs. The degree of strain relaxation of the InGaAs layer is determined by the relative thickness of the GaAs and InGaAs layers. The increase in the in-plane lattice parameter of these bonded GaAs/InGaAs/GaAs structures is 0.3-0.4%.

Characterization of solution-bonded GaAs/InGaAs/GaAs features on GaAs

“…Pseudomorphic heterostructures were grown on quarters of 2 diameter semi-insulating GaAs(0 0 1) substrates by metalorganic chemical vapor deposition (MOCVD) in an optical shower-head reactor [14]. As previously reported and shown here again in figure 1(a), the structures consist of a 50 or 100 nm thick AlAs or Al 0.7 Ga 0.3 As layer, followed by a GaAs layer, an In 0.08 Ga 0.92 As layer and a GaAs cap layer with thickness equal to that of the first GaAs layer [12,13]. The lattice mismatch strain in In 0.08 Ga 0.92 As on GaAs is 0.00568.…”

“…The as-grown layer structures were characterized by high resolution XRD to confirm the thickness of the various layers and the AlGaAs and InGaAs alloy composition [12]. Atomic force microscopy (AFM) measurements of the as-grown wafers showed an RMS roughness of 0.15 nm.…”

“…However, the misfit dislocation density is small enough that no strain relaxation was detected by XRD. AFM images of structures having a 60 nm thick InGaAs layer showed only a few discrete long, straight surface steps [12].…”

“…Threading dislocations that degrade device performance are not introduced and contamination of the surfaces to be bonded through exposure to the atmosphere, which is especially problematic for direct semiconductor to semiconductor wafer bonding, is avoided. Nominally 10 μm square bonded heterostructures were reported, with in-plane lattice constants in the range 0.3-0.4% larger than the lattice constant of GaAs [11,12]. The strain relaxation and crystal quality of the bonded features was confirmed by highresolution x-ray diffraction (XRD).…”

“…Other approaches to provide elastically-relaxed (defectfree) 'virtual substrates' include epitaxial growth on freestanding semiconductor slabs [8,9] and epitaxial growth of strained layers on a sacrificial layer that is later removed to allow elastic strain relaxation to occur [10,11]. One such approach, called in-place bonding, was first applied to achieve a strained Si layer on a Si(0 0 1) substrate [11] and more recently was demonstrated for GaAs/InGaAs/GaAs structures on GaAs(0 0 1) substrates [12,13]. In the latter case elastic strain relaxation and bonding occur during removal of a sacrificial AlAs or AlGaAs layer in a wet etch solution.…”