Dislocation Study in InGaAs QW Metamorphic Lasers

There has been a drive to produce novel InGaAs Quantum Wells (QW) on GaAs substrate lasers for telecommunication applications that can replace current InP based lasers. The In concentration in the InGaAs QW can be fine-tuned so that the emission is in the C-band (1330nm) or O-band (1550nm) telecommunication bands. Furthermore, compared to the current InP substrates, GaAs is less brittle, cheaper and available large wafer sizes: making them ideal for mass fabrication ¹. Difficulties can arise due to lattice mismatches between the InGaAs QW and GaAs substrate, which causes an increase in non-radiative recombination centres (whereby phonons instead of photons are produced) ². One proposal that has been used to overcome this problem is metamorphic growth, where a buffer layer is grown between the substrate and active region. In turn, this creates an artificial substrate with a lattice constant that can be tailored to greatly reduce the lattice mismatch between active region and substrate.<br/><br/>In the metamorphic buffer layer, strain is relieved via the creation of dislocations. These dislocations are confined to a certain region within the metamorphic buffer ³. It is well known that these can be classified in many ways such as 60° or 90° (pure edge) dislocations and it is common for the burgers vectors to be identified using techniques such as weak beam dark -field transmission electron microscopy ^4,5. However, to date, few studies have provided in-depth details on the distribution of the type dislocations within an InGaAs metamorphic buffer and how this could be linked to the performance of the laser.<br/><br/>This work investigates a series of InGaAs QWs on GaAs substrate metamorphic lasers grown by Metal Organic Vapour Phase Epitaxy (MOVPE) using transmission electron microscopy techniques. This study identifies and characterises properties of dislocations within the metamorphic buffer. We also address the In concentration of the metamorphic buffer which these dislocations are based around.<br/><br/>Finally, our data elaborates further on the distribution of the dislocations. These findings lend themselves towards the understanding of laser emission behaviour and the mechanism of relaxation in the buffer. In turn, allowing novel metamorphic lasers to be manufactured with characteristics similar to current commercial semiconductor lasers.<br/><br/><b>ACKNOWLEDGEMENTS</b><br/><br/>This work was supported by the Engineering and Physical Sciences Research Council (Grant number EP/S023321/1)<br/><br/><b>REFERENCES</b><br/><br/>[1] E. Mura et. al., “The Importance of overcoming MOVPE surface evolution instabilities for &gt;1.3µm metamorphic lasers on GaAs”, Crystal growth and Design, <b>21</b>, 4 (2021)<br/><br/>[2] I. Tångring <i>et. al</i>., “Metamorphic growth of 1.25–1.29μm InGaAs quantum well lasers on GaAs by molecular beam epitaxy”, Journal of Crystal Growth, <b>301-302</b>, (2007).<br/><br/>[3] B. Müller et. al., “Zn_0.85Cd_0.15Se active layers on graded-composition In_xGa_1−xAs buffer layers”, Journal of Applied Physics, <b>85</b>, 12 (1999).<br/><br/>[4] Y.Chen <i>et. al.</i>, “Structure and location of misfit dislocations in InGaAs epilayers grown on vicinal GaAs(001) substrates”, Applied Physics Letters. <b>62</b>, 13 (1993).<br/><br/>[5] S. Tavakoli <i>et. al.</i>, “Tilt generation in step-graded In_{&lt;span style="font-size:10.8333px"&gt;x&lt;/span&gt;}Ga_1−xAs metamorphic pseudosubstrate on a singular GaAs substrate using a low-temperature grown InGaP interlayer”, Journal of Applied Physics. <b>103</b>, 10 (2008).