Electrical and optical characteristics of AlAsSb/GaAsSb distributed Bragg reflectors for surface emitting lasers

Abstract

We demonstrate an undoped 20 1 2 pair AlAsSb/GaAsSb distributed Bragg reflector ͑DBR͒ grown lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.78 m with a maximum reflectivity exceeding 99%. We also measure current-voltage characteristics in a similar 10 1 2 period p-type DBR and find that a current density of 1 kA/cm 2 produces a 2.5 V drop. Hole mobilities and doping concentrations in AlAsSb and GaAsSb are also reported. © 1995 American Institute of Physics.Vertical-cavity surface-emitting lasers ͑VCSELs͒ have been demonstrated at a variety of wavelengths shorter than 1 m. 1,2 They have found many useful applications from short haul optical links to printing. Demonstration of similar devices at wavelengths longer than 1 m has been more problematic. This is because refractive index differences ͑⌬n͒ are relatively small between materials in the InGaAsP system, which is most commonly used in this wavelength range, and the distributed Bragg reflector ͑DBR͒ optical performance depends on ⌬n between the mirror layers. One approach to this problem has been wafer bonding of GaAs/AlGaAs DBRs to InP/InGaAsP active regions. In this manner, pulsed 1.3 ͑Ref. 3͒ and 1.55 m ͑Ref. 4͒ VCSELs have been demonstrated. Progress has also been made using thermally conductive dielectric mirrors. 5 An alternative all-epitaxial approach consists of using DBRs composed of antimonide compounds, which can be lattice matched to InP and have a high refractive index contrast.Recently, several groups have demonstrated highly reflective DBRs incorporating various antimonide compounds including: AlPSb/GaPSb on InP, 6 GaAsSb/AlAsSb on InP, 7 and AlGaAsSb/AlAsSb on InP. 8,9 All these structures were undoped, however, whereas an electrically injected VCSEL usually employs at least one doped semiconductor mirror. The issues of doping in these materials have not been explored in the context of DBR optical properties and electrical transport. As with VCSELs emitting at shorter wavelengths, the properties of doped DBRs can have a fundamental effect on the VCSEL performance, due to free carrier loss and thermal dissipation in the mirror. These are particularly critical for the p-type mirror, because of lower hole mobility and larger effective masses.In this letter, we report the highest demonstrated reflectivity for an undoped GaAsSb/AlAsSb DBR ͑RϾ99%͒, as well as a p-type GaAsSb/AlAsSb DBR and its optical and electrical characteristics. Both mirrors were grown by molecular beam epitaxy ͑MBE͒ lattice matched to InP with center wavelengths at 1.78 and 1.74 m, respectively. The main advantage of this material system is a large ⌬nϳ0.5, which enables fabrication of DBRs with relatively few mirror pairs and allows higher ultimate reflectivities in the presence of free carrier absorption. Lattice matching to InP also facilitates compatibility with the more mature InGaAs/InGaAsP materials for the active region. Shifting the absorption edge of the high refractive index layer toward shorte...

Molecular beam epitaxy of InP-based alloys for long-wavelength vertical cavity lasers

“…9 We controlled the composition of the AlGaAsSb alloy via short-period superlattices ͑2.0 nm͒ with varying duty cycles of AlAsSb and GaAsSb. Using this method we formed alternating 1 / 4 layers of Al 0.95 Ga 0.05 As 0.54 Sb 0.46 and Al 0.30 Ga 0.70 As 0.52 Sb 0.48 , referred to in this article as 95%AlGaAsSb and 30%AlGaAsSb, respectively.…”

Fabrication of a GaAsSb/AlAsSb distributed Bragg reflector with a highly stacked InAs quantum dash structure on InP(001) substrate

“…However, a high-reflection mirror such as a distributed Bragg reflection (DBR) mirror needs to be realized in order to fabricate a high-performance SESAM or VCSEL, but it is difficult to fabricate DBR mirrors on InP substrates because of the small difference between the refractive indexes of lattice-matched InGaAs and InAlAs. As a result, we investigated the fabrication of a DBR mirror using GaAsSb/AlAsSb with a large difference in the refractive index [12,13].…”

High-power single-mode 1330- and 1550-nm VCSELs bonded to silicon substrates

“…AlGaAsSb DBRs can be grown epitaxially on InP but so far, MBE is the only is the only material growth technology that has produced mirrors using this compound. 1 AlAs/GaAs DBRs have very attractive properties in terms of index contrast and thermal conductivity but these are not lattice-matched to InP. To combine an AlAs/GaAs DBR with an InGaAsP active region, it is necessary to resort to wafer bonding 2 or metamorphic growth.…”