PbSe quantum well mid-infrared vertical external cavity surface emitting laser on Si-substrates

Abstract

Mid-infrared vertical external cavity surface emitting lasers based on PbSe/PbSrSe multi-quantum-well structures on Si-substrates are realized. A modular design allows growing the active region and the bottom Bragg mirror on two different Si-substrates, thus facilitating comparison between different structures. Lasing is observed from 3.3 to 5.1 μm wavelength and up to 52 °C heat sink temperature with 1.55 μm optical pumping. Simulations show that threshold powers are limited by Shockley-Read recombination with lifetimes as short as 0.1 ns. At higher temperatures, an additional threshold power increase occurs probably due to limited carrier diffusion length and carrier leakage, caused by an unfavorable band alignment.

Temperature dependent band offsets in PbSe/PbEuSe quantum well heterostructures

“…From the fit of the experimental data, the normalized conduction band offset is determined as 0:4560:15 of the band gap difference, independently of Eu content up to 14% and temperature from 20 to 300 K. Lead salt heterostructures have been extensively used for fabrication of coherent mid-infrared light sources such as buried stripe lasers, 1,2 vertical cavity surface emitting lasers, 3,4 microdisk lasers, 5,6 photonic crystal lasers, 7 as well as external cavity disk lasers with tunable emission and high output powers. [8][9][10][11] In these devices, ternary lead salt alloys with Sr or Eu are usually employed as barriers for the quantum wells (QWs), providing a large tunability of the bands gaps E g as required for band gap engineering. As a result, room temperature mid-infrared laser operation in cw-mode has been achieved at wavelengths up to 4:3lm.…”

In-well pumped mid-infrared PbTe/CdTe quantum well vertical external cavity surface emitting lasers

“…In contrast to a monolithic bottom chip, a modular 2014) bottom chip allows to operate the device over a much large temperature range, 12 which helps to identify the contribution of various carrier loss mechanisms to the threshold power. The threshold condition for lasing is expressed by…”

“…As a result, contrary to conventional lead salt VECSELs, the thickness of the active structure is not limited by the carrier diffusion length in the barrier. 12 Hence, the in-well pump scheme allows to use active structures containing many QWs. Furthermore, since the wide-gap CdTe provides a very large carrier confinement in QWs, thermal leakage of charge carriers, which has been supposed to limit the laser performance of PbSe/PbSrSe QW VECSELs at higher temperature, 12 can be excluded.…”

“…12 Hence, the in-well pump scheme allows to use active structures containing many QWs. Furthermore, since the wide-gap CdTe provides a very large carrier confinement in QWs, thermal leakage of charge carriers, which has been supposed to limit the laser performance of PbSe/PbSrSe QW VECSELs at higher temperature, 12 can be excluded. Moreover, the PbTe/CdTe material system is not only restricted to the fabrication of QW structures but also it is quite promising for fabrication of quantum dots that may be also employed in VECSELs.…”

“…The barrier layers are made of ternary materials, such as PbXSe or PbXTe (X ¼ Sr, Eu). [12][13][14] The external cavity arrangement of VECSELs permits a simple optical pump scheme, where electron-hole pairs are generated in the spacer/barrier layers and then captured by QWs. Since for VECSLEs no doping is required, optical pumping leads to a substantial reduction of free carrier absorption in the mid-IR.…”