The ability to create metamorphic hybrid heterostructure of 1300 nm spectral band VCSEL is demonstrated. Metamorphic semiconductor part of heterostructure with GaAs/AlGaAs DBR and InAlGaAs/InGaAs QW active region has been grown by molecular beam epitaxy (MBE) on GaAs (100). Top dielectric SiO2/Ta2O5 DBR is made by the magnetron sputtering method. VCSEL has been studied under optical pumping (λ = 532 nm, diameter of the focused laser beam of ~ 1 μm) by using micro-PL setup in the range of optical pump power 0 – 70 mW at room temperature. Presence of the superlinear PL intensity growth having threshold-like dependence of PL integral intensity together with the PL peaks narrowing and mode composition modification with the pumping density increasing could be attributed to lasing behavior of the structure. Obtained results indicate the opportunity to use metamorphic growth on GaAs substrates for the 1300 nm range VCSEL manufacturing.
In this work, electrically-injected microdisk lasers with diameter varied from 15 to 31μm based on an InAs/InGaAs QD
active region have been fabricated and tested in continuous wave regime. At room temperature, lasing is achieved at
wavelength around 1.26…1.27 μm with threshold current density about 900 A/cm2. Specific series resistance is
estimated to be about 10-4 Ohm•cm2. The lasers were tested at elevated temperatures. Lasing is achieved up to 100°C
with threshold current of 13.8mA and lasing wavelength of 1304nm in device with 31μm diameter. To the best of our
knowledge, this is the highest CW lasing temperature and the longest lasing wavelength ever reported for injection QD
microdisk/microring lasers on GaAs substrates. Emission spectrum demonstrates single-mode lasing with side mode
suppression ration of 24dB and dominant mode linewidth of 35pm. The far field radiation pattern demonstrates two
narrow maxima off the disk plane. A combination of device characteristics achieved (low threshold, long wavelength,
operation at elevated temperatures) makes them suitable for application in future optoelectronic circuits for optical
interconnect systems.
A concept of passive cavity surface–emitting laser is proposed aimed to control the temperature shift of the lasing
wavelength. The device contains an all–semiconductor bottom distributed Bragg reflector (DBR), in which the active
medium is placed, a dielectric resonant cavity and a dielectric top DBR, wherein at least one of the dielectric materials
has a negative temperature coefficient of the refractive index, dn/dT < 0. This is shown to be the case for commonly used
dielectric systems SiO2/TiO2 and SiO2/Ta2O5. Two SiO2/TiO2 resonant structures having a cavity either of SiO2 or TiO2
were deposited on a substrate, their optical power reflectance spectra were measured at various temperatures, and
refractive index temperature coefficients were extracted, dn/dT = 0.0021 K-1 for SiO2 and dn/dT = –0.0092 K-1 for TiO2.
Using such dielectric materials allows designing passive cavity surface–emitting lasers having on purpose either positive,
or zero, or negative temperature shift of the lasing wavelength dλ/dT. A design for temperature–insensitive lasing
wavelength (dλ/dT = 0) is proposed. Employing devices with temperature–insensitive lasing wavelength in wavelength
division multiplexing systems may allow significant reducing of the spectral separation between transmission channels
and an increase in number of channels for a defined spectral interval enabling low cost energy efficient uncooled devices.
Detailed investigation of anomalous modal behavior in fabricated bottom-emitting intra-cavity contacted 960 nm range
vertical cavity surface emitting lasers (VCSELs) have been performed. At low currents the broad-aperture VCSELs show
multi-mode operation at 945 nm via whispering gallery-like modes. Subsequent increase of pump current results in rapid
increase of fundamental mode intensity and switching to a pure single transverse mode lasing regime at 960 nm with the
higher slope efficiency. As a result record single transverse mode output power of 15 mW with a side-mode-suppressionratio
(SMSR) above 30 dB was achieved. The observed phenomena cannot be explained by oxide-index guiding or
changes in current pumping. 2D heat transport simulations show a strong temperature gradient inside the microcavity
due to an effective lateral heat-sinking. This creates an effective waveguide and results in lower optical losses for the
fundamental mode. At fixed pump current in pulsed regime (pulse width < 400 ns) high-order modes dominate, however
the subsequent increase of pulse width leads to a rapid rise of optical power for the fundamental mode and SMSR
increasing. Thus the self-heating phenomena play a crucial role in observed VCSEL unusual modal behavior.
We present L-I, I-V and spectral characteristics at 300 and 77 K of the flip-chip LED arrays based on p-InAsSbP/n-
InGaAsSb heterostrucutres with photonic crystal formed onto an outcoupling n+-InAs substrate. We also describe results
on IR imaging (2D radiation mapping) and near and far field patterns in forward biased LEDs.
InGaAsSb narrow gap heterostructures with p-InAsSbP claddings grown onto heavily doped n+-InAs substrates have
been processed into 70 μm wide square mesas lined in a 1x4 array with individual addressing of elements. We report I-V,
L-I characteristics of the array as well as IR images allowing characterization of cross talk, reflectance of the contacts
and apparent temperatures in the spectral range around 3.6 μm. Reflectance and outcoupling efficiency is presented for
photonics crystal structures with regard to their implementation in LED assemblies.
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