Optimization of InGaP metamorphic buffers grown by MOVPE

Dislocation distributions and tilts in Al(Ga)InAs reverse-graded layers grown on misorientated GaAs substrates

“…In III-V lattice-mismatched heteroepitaxy, eight dislocation slip systems can be activated and the metamorphic Al(Ga)InAs buffers relieve their strain mostly by formatting a misfit dislocation of a/2⟨110⟩{111}. [12] The burgers vectors of a/2⟨101⟩-type dislocations do not sit perfectly on their [110] or [1][2][3][4][5][6][7][8][9][10] line direction but are leaning off towards the [001] direction. These burgers vectors can be resolved into three parts, i.e., an edge component, a screw component both in ⟨110⟩, and another tilt component in ⟨001⟩.…”

“…Otherwise, the surface normal of the epilayer will tilt away from [001]. Two types of 60 ∘ dislocations exist, i.e., [1][2][3][4][5][6][7][8][9][10] α and [110] β dislocations, both exist at compressively stressed interfaces, presumably with Gaand As-as their dislocation cores, respectively. The difference in the core structures of α and β dislocations leads to a significant difference in their activation energy for nucleation, as well as for their movements, as shown in Table 1.…”

“…To obtain high quality Al(Ga)InAs buffers, it is nec-essary to investigate and understand the properties of dislocations formed during the strain-relaxation process. Our experiments present that the dislocation distributions and tilts in [110] and [1][2][3][4][5][6][7][8][9][10] directions of the compositionally undulating Al(Ga)InAs differ from those of the conventional step-graded samples, which are attributed to the different effects of the reverse-graded layer on α and β dislocations.…”

“…Line In our experiments, the FWHMs of the symmetric (004) XRC for InP/Al(Ga)InAs buffers were measured using the x-ray incident along the two ⟨110⟩ directions. Broadening of the FWHM corresponding to the x-ray beam along the [110] and [1][2][3][4][5][6][7][8][9][10] directions is observed, which is mainly induced by α and β dislocations, respectively. [16] Figure 1 shows that the FWHMs of (004) XRCs of sample A are larger than those of sample B in the [110] direction, while an opposite tendency is observed in the perpendicular direction.…”

“…[2] Various metamorphic buffers are often grown with the composition of the compound changing linearly [3] or by steps, [4] and the application of graded buffers helps to reduce the threading dislocation density (TDD) which could otherwise degrade the performance of the devices. Among the used metamorphic buffer materials, [5][6][7] the Al(Ga)InAs alloy system is found to be quite efficient in achieving high performance in optoelectronic devices. Such performance is similar to or even better than what can be achieved in native InP-based devices.…”