Lynred is leading the development of infrared detectors for high performances applications. Two trends are identified in the infrared range, the increase of the operating temperature and the pixel pitch reduction. For 15 years, the III-V technologies present an increasing interest to address both challenges. At LYNRED, these technologies allow to address Short Wave InfraRed (SWIR) and Mid-Wave InfraRed (MWIR) for ground applications. Many challenges have to be addressed for the future focal plane arrays (FPAs). Electrical and optical crosstalks as well as image quality and stability, are one of the prime concern for detectors with pixel pitch down to 7.5μm. In order to reach an industrial production level of infrared FPAs, technological developments are required at each steps: the epitaxy, the detector array process, flip chip and back end processing. Another key element is the Read Out Integrated Circuit (ROIC) designed in-house to fulfil our customer needs.
We review the latest developments at LYNRED on III-V technologies, in terms of operability, residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations.
Buried heterostructure (BH) lasers are routinely fabricated for telecom applications. Development of quantum cascade
lasers (QCL) for sensing applications has largely benefited from the technological achievements established for telecom
lasers. However, new demands are to be met with when fabricating BH-QCLs. For example, hetero-cascade and multistack
QCLs, with several different active regions stacked on top of each other, are used to obtain a broad composite gain
or increased peak output power. Such structures have thick etch ridges which puts severe demand in carrying out
regrowth of semi-insulating layer around very deeply etched (< 10 μm) ridges in short time to realize BH-QCL. For
comparison, telecom laser ridges are normally only <5 μm deep. We demonstrate here that hydride vapour phase epitaxy
(HVPE) is capable of meeting this new demand adequately through the fabrication of BH-QCLs in less than 45 minutes
for burying ridges etched down to 10-15 μm deep. This has to be compared with the normally used regrowth time of
several hours, e.g., in a metal organic vapour phase epitaxy (MOVPE) reactor. This includes also micro-stripe lasers
resembling grating-like ridges for enhanced thermal dissipation in the lateral direction. In addition, we also demonstrate
HVPE capability to realize buried heterostructure photonic crystal QCLs for the first time. These buried lasers offer
flexibility in collecting light from the surface and relatively facile device characterization feasibility of QCLs in general;
but the more important benefits of such lasers are enhanced light matter interaction leading to ultra-high cavity Q-factors,
tight optical confinement, possibility to control the emitted mode pattern and beam shape and substantial reduction in
laser threshold.
In this work we present a significant step toward monolithic multiplexed distributed feedback (DFB) quantum cascade
lasers (QCL) array on indium phosphide (InP). A multi-wavelength DFB-QCL array evanescently coupled to an
underlying InGaAs waveguide on iron doped InP wafer is presented. We introduce the design, optimization, simulation
and fabrication of the adiabatic coupler ensuring high transfer efficiency from the active to the passive waveguide. The
active region designed in 7 μm - 10 μm wavelength range is grown by molecular beam epitaxy on top of an InGaAs
waveguide. Components are defined during postgrowth processing, which eliminates the need for material regrowth or
bonding techniques. With the present design, one could realize a broadly tunable, mechanically robust, single-mode
output source which can be used in spectroscopic applications.
Together with the optimal basic design, buried heterostructure quantum cascade laser (BH-QCL) with semi-insulating regrowth offers a unique possibility to achieve an effective thermal dissipation and lateral single mode. We demonstrate here the realization of BH-QCLs with a single-step regrowth of highly resistive (>1×108 ohm·cm) semi-insulating InP:Fe in <45 min for the first time in a flexible hydride vapor phase epitaxy process for burying ridges etched down to 10 to 15 μm depth, both with and without mask overhang. The fabricated BH-QCLs emitting at ∼4.7 and ∼5.5 μm were characterized. 2-mm-long 5.5-μm lasers with a ridge width of 17 to 22 μm, regrown with mask overhang, exhibited no leakage current. Large width and high doping in the structure did not permit high current density for continuous wave (CW) operation. 5-mm-long 4.7-μm BH-QCLs of ridge widths varying from 6 to 14 μm regrown without mask overhang, besides being spatially monomode, TM00, exhibited wall plug efficiency (WPE) of ∼8 to 9% with an output power of 1.5 to 2.5 W at room temperature and under CW operation. Thus, we demonstrate a quick, flexible, and single-step regrowth process with good planarization for realizing buried QCLs leading to monomode, high power, and high WPE.
Together with the optimal basic design, buried heterostructure quantum cascade laser (BH-QCL) with semi-insulating regrowth offers unique possibility to achieve an effective thermal dissipation and lateral single mode. We demonstrate here for the first time realization of BH-QCLs with a single step regrowth of highly resistive (<1x108 ohm•cm) semiinsulating InP:Fe in less than 45 minutes in a flexible hydride vapour phase epitaxy process for burying ridges etched down to 10-15 μm deep both with and without mask overhang. The fabricated BH-QCLs emitting at ~4.7 μm and ~5.5 μm were characterized. 2 mm long 5.5 μm lasers with ridge width 17-22 μm, regrown with mask overhang, exhibited no leakage current. Large width and high doping in the structure did not permit high current density for CW operation. 5 mm long 4.7 μm BH-QCLs of ridge widths varying from 6-14 μm regrown without mask overhang, besides being spatially monomode, TM00, exhibited WPE of ~8-9% with an output power of 1.5 – 2.5 W at room temperature and under CW operation. Thus, we demonstrate a simple, flexible, quick, stable and single-step regrowth process with extremely good planarization for realizing buried QCLs leading to monomode, high power and high WPE.
We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm-1 with 60 cm-1 tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5μm.
We demonstrate a monolithic Quantum Cascade Laser array. We show phase-locking and single-mode emission
at λ=8.4μm. It consists of narrow ridges buried into InP:Fe. Phase-locking is provided by evanescent coupling between
adjacent ridges. This μ-structuration is simultaneously an answer to the excessive heating and poor beam quality of broad
area lasers. First, it increases the surface of exchange between the multi-layer active region and the InP:Fe, which
presents a higher thermal conductivity. Secondly, by choosing carefully the width of emitters and the distance between
them, we insure phase locking and control of the supermode emission. We have investigated 2μm wide emitters. In order
to study the behavior of evanescent coupling, we have chosen spacing from 1 to 8 microns. The number of emitters
ranges from 1 to 64. Technological feasibility was demonstrated up to 64 emitters, and lasing operation up to 32 emitters.
We have obtained a pure dual-lobe far-field pattern as expected from an anti-symmetrical supermode. The width of each
lobes narrows with an increasing array size as expected from the diffraction theory. The beam quality is insensitive to the
injective current. The optical power scales linearly with the number of emitters.
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