Mechanical strain mapping of GaAs based VCSELs

Abstract

We report an investigation of the strain field in mesa structures for oxide-confined vertical-cavity surface-emitting lasers (VCSELs) using the polarization-resolved micro-photoluminescence (PL) measurement of the degree of polarization (DOP) at room temperature. The DOP of the PL is correlated with the spatial distribution of the embedded anisotropic strain in a VCSEL structure. Measurements normal to (100) surfaces of the samples and from (110) cross-sectional planes were performed. The effect of two processes required in the fabrication of GaAs-based VCSELs was studied: the plasma etching of the P-doped distributed Bragg reflector and the wet oxidation process used to control current flow and lateral optical confinement. The DOP method allows very sensitive measurements of the mechanical strain (on the order of 10−5) accumulated in VCSEL devices even during different steps of the fabrication process.

Polarimetric photoluminescence microscope for strain imaging on semiconductor devices

“…Below the stripe, the tensile deformation within SiN x induces a compressive deformation within the substrate material. On the other hand, because of the stripe form factor, the strain along the stripe should be negligible [14]. Thus we know that in this area (i.e.…”

“…DOP is sensitive to the anisotropic part of the strain tensor, while insensitive to the isotropic (or hydrostatic) part. This approach has proven particularly efficient for the analysis of situations where the semiconductor crystal deformation is dominated by this anisotropic part [12][13][14][15]. DOP has a very good sensitivity to small anisotropic deformations, as is the case for semiconductors such as GaAs, InP and the associated ternary and quaternary compounds, which have small yield stresses.…”

Selective wet oxidation of AlAsSb alloys on GaAs

“…The variation of AlAsSb composition is therefore likely to lead to pronounced changes in the oxidation that are strain related. Among the various methods available to characterize the strain distribution in oxidized AlGaAs mesas 24,48,49,26,27,50 , we here chose to indirectly quantify the strain by simply measuring the aperture-averaged height difference at the top surface between the (unoxidized) semiconductor and the oxide. Technically, this parameter is extracted from postoxidation atomic force microscope surface profiles that are acquired in tapping mode at room temperature over ~20µm-wide square regions centered around ~8µm oxide apertures (see Fig.…”

Chemical imaging of oxide confinement layers in GaAs/AlxGa1−xAs VCSELs

“…This fabrication process raises a number of questions related to the VCSEL reliability [3]. Firstly, the oxide formation introduces tensile strain in ‡ Present address: 3SP Technologies SAS, 91625 Nozay, France the adjacent layers due to shrinkage of the AlOx compared to Al x Ga 1−x As [4]. Secondly, the chemical stability of the oxide phases present in the AlOx layer may also be an issue [5].…”