Elsevier

Journal of Crystal Growth

Volume 477, 1 November 2017, Pages 253-257
Journal of Crystal Growth

Metamorphic InAs quantum well lasers on InP substrates with different well shapes and waveguides

https://doi.org/10.1016/j.jcrysgro.2017.01.037Get rights and content

Highlights

  • Metamorphic InAs quantum well lasers were grown on InP by MBE.

  • The structure with trapezoidal quantum wells exhibited improved performances.

  • The laser performances were improved by using quaternary InAlGaAs waveguides.

  • Continuous wave lasing at 240 K has been achieved.

Abstract

The effects of well shapes and waveguide materials on InP-based InAs quantum well lasers have been investigated. The laser structures were grown on metamorphic In0.65Al0.35As buffers. A novel trapezoidal quantum well composed of InyGa1−yAs grading and InAs layer was used to improve the quality of quantum well. Quaternary In0.65Al0.2Ga0.15As waveguide was applied instead of ternary In0.65Ga0.35As to enhance the carrier injection. The material qualities have been characterized by X-ray diffraction, transmission electron microscopy and photoluminescence measurements, while the device properties of the lasers with various structures were investigated at different temperatures. Results show that the laser performances have been improved by the use of trapezoidal quantum wells and InAlGaAs 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

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