Metamorphic InAs quantum well lasers on InP substrates with different well shapes and waveguides
Introduction
Mid-infrared semiconductor lasers emitting in the wavelength range of 2–3 μm have many important applications such as molecular spectroscopy and medical diagnostics [1], [2]. They are also desired for the characterization and evaluation of photodetectors in this wavelength range [3]. Type-I InGaAsSb/Al(In)GaAsSb quantum well (QW) lasers on GaSb substrate can cover this wavelength range under continuous wave (CW) operation at room temperature (RT) [4], [5]. Also, GaSb-based interband cascade lasers (ICLs) employing type-II or type-I active regions have achieved RT CW lasing with relatively low threshold current densities at longer wavelength [6], [7].
However, compared to GaSb substrates, InP substrates offer more mature commercial growth and processing technologies as well as higher thermal conductivity. On InP, quantum cascade lasers (QCLs) have recently achieved significant advances in mid-infrared wavelength range, but the performances deteriorated dramatically as the emitting wavelength was shortened close to 3 μm as highly strained InGaAs/InAlAs growth is required to obtain large conductive band offset [8]. On the other hand, by increasing the indium (In) content in the InGaAs QW layer of conventional type-I lasers on InP and even using highly strained pure InAs QW, the lasing wavelength can be extended to 2–2.4 μm [9], [10], [11]. However, the significant strain in InAs QW on InP limits the further increase of type-I QW lasing wavelength.
By constructing metamorphic InxAl1−xAs or InAsxP1−x buffers with lattice constants larger than InP, the strain in InAs QW is able to be reduced thus thicker QW thickness can be applied, which can increase the emission wavelength to around 3 μm [12], [13], [14]. Previously, we reported 2.9 μm lasing from type-I InAs QWs on metamorphic In0.8Al0.2As/InP [15]. However, the maximum working temperature under CW operation was only 180 K and considerable spontaneous emission from InGaAs waveguide was observed, which was due to the unfavorable material quality and carrier confinement. Therefore, active regions with improved material quality and enhanced carrier confinement are required for the InP-based type-I QW lasers with this metamorphic infrastructure.
In this work, the effects of InAlGaAs or InGaAs waveguides on the performances of InP-based InAs QW lasers were investigated. Furthermore, trapezoidal QWs were applied as the active region and the performances were compared to the structures with conventional rectangular InAs QWs.
Section snippets
Experiments
The epitaxial wafers were grown on n-type (0 0 1)-oriented InP epi-ready substrates in a VG Semicon V80H gas source molecular beam epitaxy system. Cells with two heater filaments were used as In and gallium (Ga) sources and a cold-lip cell with a double-wall crucible was used as aluminum (Al) source. Arsine and phosphine gases were cracked to As2 and P2 at 1000 °C and used as group V sources.
The growth started from a 200-nm-thick InP buffer, a 100-nm-thick lattice-matched In0.53Al0.47As buffer, an
Results and discussions
Fig. 2 shows the XRD (0 0 4) ω/2θ scanning curves of the metamorphic InAs QW laser structures after etching the cap layers and about 1500-nm-thick cladding layers. For all samples the strongest peak corresponds to InP substrate, and the wide peak at around −1300 s corresponds to the cladding and waveguide layers, in which the signals of In0.65Al0.35As, In0.65Ga0.35As, or In0.65Al0.20Ga0.15As layers were merged. The envelop peak at higher angle corresponds to the InAs QWs. The lattice dynamical
Conclusion
In conclusion, InP-based InAs QW lasers with different well shapes and waveguides have been grown on metamorphic In0.65Al0.35As buffers. The quaternary InAlGaAs was used as waveguide layer instead of ternary In0.65Ga0.35As, and the maximum operation temperature under CW mode was increased from 120 K to 180 K. The laser structure using trapezoidal QWs with InAs/InyGa1−yAs grading layer and InAs layer was grown and compared to the structure with rectangular pure InAs QWs. The PL intensity has been
Acknowledgments
This work was supported by the support of the National Key Research and Development Program of China under Grant No. 2016YFB0402400, the Basic Research Program of China under Grant No. 2014CB643900, the National Natural Science Foundation of China under Grant Nos. 61334004, 61405232, 61675225 and 61605232, Youth Innovation Promotion Association CAS under Grant No. 2013155, the Shanghai Sailing Program under Grant No. 15YF1414300, and the open project of Key Laboratory of Infrared Imaging
References (16)
- et al.
GaSb-based VCSELs emitting in the mid-infrared wavelength range (2–3 μm) grown by MBE
J. Cryst. Growth
(2009) - et al.
Growth of InAs-containing quantum wells for InP-based VCSELs emitting at 2.3 μm
J. Cryst. Growth
(2007) - et al.
InAsyP1−y metamorphic buffer layers on InP substrates for mid-IR diode lasers
J. Cryst. Growth
(2010) - et al.
Lasers and photodetectors for mid-infrared 2–3 μm applications
J. Appl. Phys.
(2008) - et al.
Mid-infrared semiconductor heterostructure lasers for gas sensing applications
Semicond. Sci. Technol.
(2011) - et al.
Dark current suppression in metamorphic In0.83Ga0.17As photodetectors with In0.66Ga0.34As/InAs superlattice electron barrier
Appl. Phys. Express
(2015) - et al.
Passive mode locking of a GaSb-based quantum well diode laser emitting at 2.1 μm
Appl. Phys. Lett.
(2015) - et al.
Room-temperature mid-infrared interband cascade vertical-cavity surface-emitting lasers
Appl. Phys. Lett.
(2016)