IQE has developed a novel VCSEL technology that offers lower manufacturing costs and higher production yields, entitled IQGeVCSEL™. Conventional growth of VCSELs on large diameter (150 mm) GaAs substrates is somewhat compromised by epitaxial wafers exhibiting significant bow and warp, typically in excess of 200 µm. This large bow/warp is an inherent consequence of the lattice mismatch between the GaAs substrate and the AlGaAs constituents of the thick VCSEL DBR layers, resulting in significant residual compressive strain in the epitaxial stack that deforms the final wafer. This extreme bow and warp translates to higher VCSEL chip cost due to increased yield loss and additional processing steps required to flatten the wafer. VCSELs grown on Ge substrates we have eliminated this problem because the lattice parameter of Ge sits almost midway between those of GaAs and AlAs. Substituting a Ge substrate for GaAs for this application virtually eliminates the strain that causes this bow and warp. High performance 940 nm VCSELs grown on 150 mm diameter Ge substrates exhibit epi wafer bow and warp values <10 µm and devices fabricated from these wafers perform at least as well as similar devices fabricated from the same epi structure grown on GaAs substrates. The IQGeVCSEL technology also offers itself to longer wavelength VCSEL devices, such as those with dilute nitride active regions, where the DBR mirrors typically are thicker and therefore have even higher residual compressive strain.
Dr Johnson is a Technical Director at IQE PLC. He is leading the company’s worldwide effort in next generation VCSELs. Before taking this key strategic role within IQE, Andrew led the Solar Business unit within the Company and previously held positions as General Manager at IQE PLC’s substrate manufacturing facility, Wafer Technology, and at QinetiQ as a Research Fellow within the emerging technologies group, primarily focussed on the development and investigation of novel narrow gap III-V materials for advanced InfraRed applications.