Metalorganic vapour phase epitaxy of InGaAs/InAlAs and GaAs/AlGaAs quantum cascade laser structures

Andrey B. Krysa*a, Dmitry G. Revinb, Chris N. Atkinsb, Kenneth Kennedya, John W. Cockburnb aEPSRC National Centre for III-V Technologies, Dept. of Electronic and Electrical Engineering,

University of Sheffield, Mappin Street, Sheffield, S1 3JD, United Kingdom bDept. of Physics, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, United Kingdom

BIOGRAPHY Andrey Krysa received the M.Sc. degree in quantum electronics from the Moscow Engineering Physics Institute, Moscow, Russia, in 1990, and the Ph.D. degree from the Lebedev Physical Institute, Russian Acad. Sci., Moscow, Russia, in 1997.

In 1995, he joined the Dept. of Optoelectronics at the Lebedev Institute as a Research Scientist and performed research on II–VI compounds. During 1999–2000, he was at the Institut für Halbleitertechnik, RWTH Aachen, Germany, where he was engaged in epitaxy of ZnSe and related structures. Since joining the National Centre for III–V Technologies, Sheffield, UK, in 2001, he has been engaged in MOVPE of the group III arsenides and phosphides. His current research interests include development of quantum cascade lasers and structures based on InP quantum dots.

Dr. Krysa was awarded the Humboldt Research Fellowship in 1999 and holds the IET Optoelectronics Award 2008.

TECHNICAL ABSTRACT Metalorganic vapour phase epitaxy (MOVPE) has been successfully introduced by our group as an alternative

growth technology of mid-IR InGaAs/InAlAs/InP quantum cascade lasers (QCLs) [1, 2]. Later on, we have transferred this technology to a production type multi wafer MOVPE reactor [3]. Many research groups and industrial companies have since followed our technological approach.

The crystalline quality of the MOVPE grown material meets the stringent requirements imposed by the QCLs designs for operation in a wide spectral range of ~5-16 µm.

However, developing an epitaxial process of highly strain-compensated QCL structures for operation at shorter wavelengths of ~3-5 µm appeared to be extremely challenging. Careful tuning the growth temperature regime was used to produce 30-period In0.7Ga0.3As/In0.34Al0.66As structures with ~1.2% mismatch from InP in the individual constituent layers. Fig. 1 shows an STEM image of a part of the QCL core. The measured length of one cascaded period of 51.5 nm is identical to the intended value. The same period length was derived from the X-ray diffraction data. 10 µm wide and 3 mm long devices with as-cleaved facets operate at λ ≈ 4 µm and deliver more than 2.4 W of peak optical power from both facets at 300 K with threshold current density of 2.5 kA/cm2 (Fig. 2). The lasers operate up to at least 400 K with characteristic temperature of 153 K. The developed epitaxial process represents a solid platform for engineering strain-compensated QCLs structures for shorter emission wavelengths around 3.5 µm.

Another direction of our recent research efforts was revisiting GaAs-based QCLs to develop a robust and cost-effective growth technology of devices operating around 9 µm. InGaP and InAlP waveguides were used to improve optical confinement and reduce waveguide losses.

STEM confirmed the intended thickness of individual GaAs and Al0.45Ga0.55 layers in the laser core. The amplitude of the interface roughness is less than 0.5 nm (the nominal thickness of the thinnest layer in the active region is 0.9 nm). QCLs with In0.47Al0.53P waveguides demonstrate record low threshold current densities for the GaAs/AlxGa1-xAs materials system. Under pulsed operation, threshold current densities of 2.2 and 4.4 kA/cm2 were observed at 240 and 300 K respectively, and laser emission was maintained up to temperatures of at least 330 K. The laser emitted peak optical powers of 0.57 W at 240 K and 0.16 W at 300 K. The presented laser performance should greatly increase the prospects of mid-IR GaAs-based QCLs for technological applications.

Details, challenges and limitations of the QCL growth technology based on MOVPE will be discussed in my talk.

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Keywords: InGaAs/InAl

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