Doping-induced losses in AlAs/GaAs distributed Bragg reflectors

Abstract

We have studied n- and p-type doping-induced performance degradation of AlAs/GaAs distributed Bragg reflectors (DBRs) for applications in vertical cavity lasers (VCLs). Based on high-accuracy optical reflectance and triple-axis x-ray diffraction measurements on a variety of differently doped DBR structures grown by metalorganic vapor-phase epitaxy, a fitting procedure was employed to extract the doping-dependent optical loss. A striking observation is that the reflectance of these DBRs is much more sensitive to n- than p-type doping incorporation. While in the latter case the loss can be well accounted for by intervalence-band and free-carrier absorption, additional loss mechanisms must be considered for n-type DBRs. We relate the losses to doping-enhanced interdiffusion effects resulting in increased interface scattering. These findings should have important consequences for the design of VCLs, demonstrating the importance of reduced n-type doping concentrations and/or growth temperatures, or the application of alternative device concepts, e.g., employing intracavity contacts.

Towards electrically‐pumped microcavity polariton lasers

“…Another important issue concerns the cavity losses related to the doping of the DBRs [15]. To estimate the influence of doping on the photon confinement, we have fabricated a similar undoped microcavity structure, and compared the FWHM linewidths of the cavity modes in the two samples.…”

Optical loss and interface morphology in AlGaAs∕GaAs distributed Bragg reflectors

“…Instead we suggest, as already discussed in Ref. 3, that the reduced reflectance is due to an inhomogeneous interdiffusion process resulting in interface roughening and increased scattering loss. 3 It should be noted that the topmost GaAs surface of the DBRs after cooling down in AsH 3 ambient remains smooth, indicating that the interface roughness of the DBRs should not influence the quality of the QWs grown upon them.…”

“…By contrast, there have been reports on improved VC-SEL performance from the use of an undoped bottom DBR, 2 and in a previous study, we showed that AlAs/ GaAs DBR properties are effectively more degraded by n-type rather than p-type doping. 3 Based on detailed investigations of doping and annealing dependent x-ray diffraction ͑XRD͒ and reflectance measurements, it was argued that this degradation is due to n-type doping-enhanced Al-Ga interdiffusion effects resulting in increased interface scattering. 3 More recently, Haberland et al used reflectance spectroscopy to measure the development of interface roughness in situ during the metal-organic vapor-phase epitaxy ͑MOVPE͒ growth of a 650 nm VCSEL structure.…”

“…3 Based on detailed investigations of doping and annealing dependent x-ray diffraction ͑XRD͒ and reflectance measurements, it was argued that this degradation is due to n-type doping-enhanced Al-Ga interdiffusion effects resulting in increased interface scattering. 3 More recently, Haberland et al used reflectance spectroscopy to measure the development of interface roughness in situ during the metal-organic vapor-phase epitaxy ͑MOVPE͒ growth of a 650 nm VCSEL structure. They also noted a gradually increasing roughness in the n-type AlGaAs/ AlAs bottom DBR that was significantly reduced in the p-type DBR.…”

“…3 To study the interface morphology of the AlGaAs/ GaAs bottom mirror by tapping-mode atomic-force microscopy ͑AFM͒ using standard silicon tips, an etching method was carried out to remove the AlGaAs layer with high selectivity to the underlying GaAs layer. 9 The top GaAs layer was thereby first removed by wet chemical etching in NH 3 :H 2 O 2 solution with pH = 7.0 after which the AlGaAs layer was removed by a short dip ͑about 8 s͒ in 1.5% hydrofluoric acid ͑HF͒.…”