Optical Characterizations of VCSEL for Emission at 850 nm with Al Oxide Confinement Layers

Abstract

In-plane micro-photoluminescence (µ-PL) and micro-reflectivity measurements have been performed at room temperature by optical excitation perpendicular to the surface of two different structures: a complete vertical surface emitting laser (VCSEL) structure and a VCSEL without the upper p-type distributed Bragg reflector (P-DBR). The two structures were both laterally oxidized and measurements were made on top of oxidized and unoxidized regions. We show that since the photoluminescence (PL) spectra consist of the cumulative effect of InGaAs/AlGaAs multi quantum wells (MQWs) luminescence and interferences in the DBR, the presence or not of the P-DBR and oxide layers can modify significantly the spectrum. µ-PL mapping performed on full VCSEL structures clearly shows oxidized and unoxidized regions that are not resolved with visible light optical microscopy. Finally, preliminary degree of polarization (DOP) of the PL measurements have been made on a complete VCSEL structure before and after an oxidation process. We obtain an image of DOP measured by polarization-resolved µ-PL. These measurements allow us to evaluate main components of strain.

Degree of polarization of luminescence from GaAs and InP as a function of strain: a theoretical investigation

“…Recently, Mokhtari et al [27] used the DOP of photoluminescence technique to investigate the occurrence of mechanical stress in vertical cavity surface emitting lasers (VCSELs), designed for emission at 850 nm, in relation to the lateral oxidation process used to control current injection and lateral optical confinement. Landesman et al [28,29] used the same technique to quantify the anisotropic stress introduced in InP or GaAs substrates by the presence of thin and narrow dielectric stripes on (100) surfaces.…”

Mechanical strain mapping of GaAs based VCSELs

“…Fig. 1 tion, the PL signal collected on top of the mesa is mainly coming from the Al 0.12 Ga 0.88 As layers of the P-DBR 12 . By symmetry, the presence of interfaces parallel to the (100) surface does not impact the DOP.…”

“…The excitation spot size was about 2 µm and the estimated power density with the use of a 20x magnification objective was close to 1 kW/cm². Theory and technical details on this technique can be found in [12][13][14][15] .…”

Polarimetric photoluminescence microscope for strain imaging on semiconductor devices

“…In our case, the stressor is a SiN x thin film deposited at the GaAs surface with a built-in stress resulting from the deposition process. We have already performed and published a detailed study of this kind of sample [13]. The SiN x thin film is deposited using plasma enhanced chemical vapor deposition (PECVD) at 280 °C.…”

“…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.…”