Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements

Abstract

Articles you may be interested inDetecting and tuning anisotropic mode splitting induced by birefringence in an InGaAs/GaAs/AlGaAs verticalcavity surface-emitting laser J. Appl. Phys. 111, 043109 (2012) We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 6 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 6 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 6 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 lm target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs. V C 2012 American Institute of Physics.[http://dx

Non-destructive Photo-modulated Reflectance Study of GalnAsSb- based VCSEL

“…EQW increases with cooling via the band gap energy (but faster than ECM at ~29.2meV/K)). Since EQW<ECM at RT, then EQW crosses and comes into resonance with ECM with increasing temperature [3][4][5]. Sample A has a higher energy feature (filled squares) which we interpret as EQW, but which became unobservable above 125K.…”

Characterization of 2.3 μm GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance

“…Since E CM decreases more slowly with increasing temperature than E QW , and E QW > E CM at 9 K, then E QW may be made to cross over and be tuned into resonance with E CM by heating from 9 K. 5,7,10 This may be observed in the temperature dependent PR measurements which were performed at the same time as the normalised reflectivity measurements of Fig. 2.…”

“…In contrast, de 1 has an essentially absorptive (symmetric) form near E QW while de 2 is dispersive (anti-symmetric). 5,7 The product of these pairs of lineshapes in Eq. (1) results in a rather complicated interplay between the symmetries and intensities of the four features.…”

“…[1][2][3] The major challenge in achieving efficient lasing in VCSELs is strongly dependent on the wavelength alignment between the peak of the gain spectrum of the active quantum well (QW) layers and the cavity mode (CM) dip in the reflectance spectrum of the VCSEL Fabry-Perot structure. 4,5 When other effects such as self-heating and non-radiative recombination have been taken into account, achieving an optimized alignment at the desired operating temperature between the energy positions of the QW ground-state transition (E QW ) and the CM dip in the reflectance spectrum (E CM ) should give improved device performance. 6 It is thus critical to know the initial E CM /E QW alignment especially with respect to the temperature performance of devices.…”

“…6 It is thus critical to know the initial E CM /E QW alignment especially with respect to the temperature performance of devices. 5 Therefore, it is important to be able to monitor the degree of any such misalignment, ideally prior to fabricating the devices from the as-grown VCSEL structure wafers, for example, so that optimum wafer positions can be determined for device selection. We report here on non-destructive optical spectroscopic studies of pre-fabrication 2.3 lm VCSEL wafers, in order to determine the effects of detuning the reflectance spectrum CM dip and QW ground-state transition energy, without having to process them into working devices.…”