Veeco MOCVD solutions are capable of supporting multiple substrates (GaAs, InP, sapphire, Si), and offer seamless transition to larger substrate sizes. For 6” GaAs red micro LED, Lumina® has demonstrated total population wavelength yield of >95% in 3 nm bin with defectivity <0.5 / cm2 @ >2um and 25% higher throughput than other platforms. For 6” sapphire miniLED, EPIK® has demonstrated within wafer wavelength 1sigma uniformity of 0.68nm (blue) / 1.24nm (green). For microLED on 200mm and 300mm silicon, Veeco has developed Propel® single wafer reactor for best in-class uniformity. Details of the technology and current data will be discussed.
We’ve developed a next-generation MOCVD platform for high-performance, commercial VCSEL production. The tool is capable of achieving total population uniformity >95% yield in +/- 3nm bin on 6” GaAs. In addition, the tool is capable to go >300 runs between maintenance while maintaining very fast growth rate up to 4.2micron / hr and low [C] impurity <2E17 cm-3. Another parameter critical to VCSEL is defectivity, where <0.5 defects / cm2 @ >2 micron size have been demonstrated. Correlation of epi and VCSEL device parameters such as threshold current density (Jth) and power conversion efficiency will be discussed.
We report on green-emitting In0.18Ga0.82N/GaN multi-quantum well (MQW) structures over a variety of metalorganic chemical vapor deposition (MOCVD) growth conditions to examine the morphology, optical quality, and micron-scale emission properties. The MOCVD growth parameter space was analyzed utilizing two orthogonal metrics which allows comparing and optimizing growth conditions over a wide range of process parameters: effective gas speed, S*, and effective V/III ratio, V/III*. Optimized growth conditions with high V/III, low gas speed, and slow growth rates resulted in improved crystal quality, PL emission efficiency, and micron-scale wavelength uniformity. One of the main challenges in green MQWs with high Indium content is the formation of Indium inclusion type defects due to the large lattice mismatch combined with the miscibility gap between GaN and InN. An effective way of eliminating Indium inclusions was demonstrated by introducing a small fraction of H2 (2.7%) in the gas composition during the growth of high temperature GaN quantum barriers. In addition, the positive effects of employing an InGaN/GaN superlattice (SL) underlayer to crystal quality and micron-scale emission uniformity was demonstrated, which is of special interest for applications such as micro-LEDs.
Improvement of light extraction efficiency of InGaN light emitting diodes (LEDs) using polydimethylsiloxane (PDMS)
concave microstructures arrays was demonstrated. The size effect of the concave microstructures on the light extraction
efficiency of III-Nitride LEDs was studied. Depending on the size of the concave microsturctures, ray tracing
simulations show that the use of PDMS concave microstructures arrays can lead to increase in light extraction efficiency
of InGaN LEDs by 1.4 to 1.9 times. Experiments utilizing 1.0 μm PDMS concave microstructures arrays demonstrated
1.60 times improvement in light extraction, which is consistent with simulated improvement of 1.63 times. The
enhancement in light extraction efficiency is attributed to increase in effective photon escape cone due to PDMS concave
microstructures arrays, and reduced Fresnel reflection within the photon escape cone due to the grading of refractive
index change between GaN / PDMS / air interface.
Staggered InGaN quantum wells (QWs) are analyzed as improved active media based on a 6-band k•p method taking
into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier
screening effect. The growths of staggered InGaN QW emitting at green regime were conducted by employing graded
temperature profile. The electroluminescence measurement shows a significant enhancement of the output power of the
staggered InGaN QW LED as compared to that of the conventional InGaN QW LED.
Staggered InGaN quantum wells (QWs) are analyzed as gain media for laser diodes to extend the lasing wavelength
towards 500 nm. The calculation of band structure is based on a 6-band k•p method taking into account the valence band
mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered
InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to
enhance the optical gain for laser diodes emitting in the green regime.
The concept of polarization engineering of InGaN quantum wells are discussed as an approach for improving the
radiative recombination rate of III-Nitride based active region. Two quantum wells were discussed as follow: 1) staggered InGaN quantum well, and 2) type-II InGaN-GaNAs quantum well. Staggered InGaN quantum wells (QW) grown by metalorganic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's Golden Rule indicates that InGaN QW with
step-function like In distribution leads to significantly improved
radiative recombination rate and optical gain due to increased electron-hole wavefunction overlap, in comparison to that
of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were
calculated based on energy dispersion and transition matrix element obtained by 6-band <b>k•p</b> formalism for wurtzite
semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields.
The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in
good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of
425-nm and 500-nm. Experimental results of light emitting diode (LED) structures at 450-nm utilizing staggered InGaN
QW show improvement in output power much higher than what is predicted theoretically. In addition to the staggered
InGaN QW, type-II InGaN-GaNAs QW was also investigated theoretically with potential of implementation for high efficiency
LEDs.
Staggered InGaN quantum wells (QW) grown by metalorganic chemical vapor deposition was demonstrated as
improved active region for visible light emitters. Fermi's Golden Rule indicates that InGaN QW with step-function like
In distribution leads to significantly improved radiative recombination rate and optical gain due to increased electronhole
wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both
conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element
obtained by 6-band k•p formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain
effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed
enhancement of radiative recombination rate, which is in good agreement with photoluminescence and
cathodoluminescence measurements at emission wavelength regime of 425-nm and 500-nm. Experimental results of
light emitting diode (LED) structures at 45-nm utilizing staggered InGaN QW show improvement in output power
much higher than what is predicted theoretically. Reduction in non-radiative recombination rate due to improved
materials quality, in addition to the enhancement in radiative recombination rate in the staggered InGaN QW could
presumably be the reason behind this significant output power improvement.
Strain-compensated InGaN quantum well (QW) active region employing tensile AlGaN barriers was analyzed as
improved gain media for laser diodes emitting at 430-440 nm by taking into account the carrier screening effect. The use
of strain-compensated InGaN-AlGaN structure is advantageous because the tensile barriers compensate the compressive
strain in the InGaN QW and the larger band offset allows high temperature operation. The band structure is calculated by
using a 6-band k times p formalism, taking into account valence band mixing, strain effect, spontaneous and piezoelectric
polarizations. The carrier screening effect is incorporated in the calculation, which is solved self-consistently. The
spontaneous emission spectra show a significant improvement of the radiative emission for strain-compensated structure.
The optical gain analysis shows enhancement in the peak optical gain for the strain-compensated QW structures.
Threshold analysis of both the conventional InGaN-GaN QW and strain-compensated InGaN-AlGaN QW active regions
indicate a reduction in the threshold carrier density and threshold current density for diode laser employing the strain-compensated
QW as its active region.
We demonstrated and analyzed 480-nm emitting III-Nitride LEDs using SiO2/polystyrene (PS) microlens arrays,
deposited via rapid-convective-deposition. Output power of MOCVD-grown InGaN QW LEDs with SiO2/PS microlens
exhibited improvement of 219%. Numerical simulation of the light extraction efficiency optimization of III-Nitride
LEDs with SiO2/PS microlens was carried out using Monte Carlo ray tracing including 3D self-consistent photon-carrier
interaction. The light extraction efficiency of the LEDs with microlens array is optimized for the PS layer thickness and
the SiO2 microspheres diameter. The simulations show good agreement with experiments, indicating the use of SiO2/PS
microlens leads to increased photon escape cone.
Design analysis of III-Nitride based intersubband quantum well absorption in the mid-IR regime (&lgr; ~ 3-5 &mgr;m) is
presented. The use of lattice-matched AlInGaN materials is advantageous because of its extremely fast intersubband
relaxation time &tgr;rel ~ 150-fs. The ability to engineer lattice-matched AlInGaN layer with GaN should allow realization of
multiple pairs of AlInGaN / GaN quantum well structures, which would otherwise be challenging due to the cracking
issues that might develop in conventional multiple pairs AlGaN / GaN heterostructures. The large conduction band offset
in III-Nitride heterostructures is also beneficial for minimizing dark current and thermal noise.
Here we present a full 3-D numerical model based on Quantum-Finite-Difference-Time-Domain (Q-FDTD) method,
with Perfectly Matched Layer (PML) boundary condition, as a versatile tool to accurately analyze 3-D QD nanostructure
with arbitrary shape. Model solid theory has been utilized to determine the 3-D band lineup of the QD heterostructure.
The effects of strain distribution, and effective mass distribution on the band structure of the QD nanostructure are also
taken into account in the model. The Q-FDTD computation has been applied for analyzing MOCVD-grown InGaAs
QDs with GaAs1-xPx barriers on GaAs. The Q-FDTD simulation, using the QDs shape measured by TEM and AFM,
shows good agreement with the experimental results obtained from the as-grown InGaAs QDs with GaAs1-xPx barriers.
We present and analyze a new nitride-based gain media by utilizing type-II InGaN-GaNAs quantum well (QW) on GaN.
This novel III-N based type-II QW allows extension of the emission wavelength from blue regime (450-nm) to yellow
regime (550-nm) with relatively-low In-content in the QW, while maintaining a large electron-hole wavefunction
overlap. High electron-hole wavefunction overlap (≥ 65%-70%) can be obtained by careful energy band engineering to
take advantage of the polarization-induced electric field. Our analysis shows this new type-II QW gain media offers
wide emission wavelength coverage, from pure blue (~450-nm) to yellow-green (~530-nm). Design and optimization for
pure blue (~450-nm), green (~515-nm) and yellow-green (~530-nm) emission structures are also presented. This method
may allow realization of green laser diode on GaN, as well as paving the way to low cost, truly monolithic solid-state
white light source.
Novel method to realize 1300-1550 nm InGaAsNSb quantum well (QW) structure on GaAs substrate is presented and analyzed. The proposed method is based on nitrogen-based inter-diffusion from InGaAsN nanometers-thick barriers into InGaAsSb quantum well layer. This method should allow realization of InGaAsNSb quantum well layer, in particular by metalorganic chemical vapor deposition (MOCVD), which would otherwise be very challenging due to the conflicting nature of optimum epitaxy parameters / conditions that nitride-based and antimonide-based compounds require.
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