We present and compare the existing methods of heteroepitaxy of III-Vs on silicon and their trends. We focus on the epitaxial lateral overgrowth (ELOG) method as a means of achieving good quality III-Vs on silicon. Initially conducted primarily by near-equilibrium epitaxial methods such as liquid phase epitaxy and hydride vapour phase epitaxy, nowadays ELOG is being carried out even by non-equilibrium methods such as metal organic vapour phase epitaxy. In the ELOG method, the intermediate defective seed and the mask layers still exist between the laterally grown purer III-V layer and silicon. In a modified ELOG method called corrugated epitaxial lateral overgrowth (CELOG) method, it is possible to obtain direct interface between the III-V layer and silicon. In this presentation we exemplify some recent results obtained by these techniques. We assess the potentials of these methods along with the other existing methods for realizing truly monolithic photonic integration on silicon and III-V/Si heterojunction solar cells.
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.
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.
A simple method of growing large areas of InP on Si through Epitaxial Lateral Overgrowth (ELOG) is
presented. Isolated areas of high quality InP suitable for photonic integration are grown in deeply etched SiO2
mask fabricated using conventional optical lithography and reactive ion etching. This method is particularly
attractive for monolithically integrating laser sources grown on InP with Si/SiO2 waveguide structure as the
mask. The high optical quality of multi quantum well (MQW) layers grown on the ELOG layer is promisingly
supportive of the feasibility of this method for mass production.
Epitaxial Lateral Overgrowth has been proposed as a key technology of a novel hybrid integration platform
for active silicon photonic components. By fabricating silicon oxide mask on top of a thin InP seed layer, we
can use the so called defect necking effect to filter out the threading dislocations propagating from the seed
layer. By optimizing the process, thin dislocation free InP layers have been successfully obtained on top of
silicon wafer. The obtained characterization results show that the grown InP layer has very high quality,
which can be used as the base for further process of active photonic components on top of silicon.
There is an intense interest on integration of III-V materials on silicon and silicon-on-insulator for realisation of optical
interconnects, optical networking, imaging and disposable photonics for medical applications. Advances in photonic
materials, structures and technologies are the main ingredients of this pursuit. We investigate nano epitaxial lateral
overgrowth (NELOG) of InP material from the nano openings on a seed layer on the silicon wafer, by hydride vapour
phase epitaxy (HVPE). The grown layers were analysed by cathodoluminescence (CL) in situ a scanning electron
microscope, time-resolved photoluminescence (TR-PL), and atomic force microscope (AFM). The quality of the layers
depends on the growth parameters such as the V/III ratio, growth temperature, and layer thickness. CL measurements
reveal that the dislocation density can be as low as 2 - 3·107 cm-2 for a layer thickness of ~6 μm. For comparison, the
seed layer had a dislocation density of ~1·109 cm-2. Since the dislocation density estimated on theoretical grounds from
TRPL measurements is of the same order of magnitude both for NELOG InP on Si and on InP substrate, the dislocation
generation appears to be process related or coalescence related. Pertinent issues for improving the quality of the grown
InP on silicon are avoiding damage in the openings due to plasma etching, pattern design to facilitate coalescence with
minimum defects and choice of mask material compatible with InP to reduce thermal mismatch.
Integration of III-V materials on silicon wafer for active photonic devices have previously been achieved by growing
thick III-V layers on top of silicon or by bonding the III-V stack layers onto a silicon wafer. Another way is the epitaxial
lateral overgrowth (ELOG) of a thin III-V material from a seed layer directly on the silicon wafer, which can be used as
a platform for the growth of active devices. As a prestudy, we have investigated lateral overgrowth of InP by Hydride
Vapor Phase Epitaxy (HVPE) over SiO2 masks of different thickness on InP substrates from openings in the mask.
Openings which varied in direction, width and separation were made with E-beam lithography allowing a good
dimension control even for nano-sized openings (down to 100 nm wide). This mimics overgrowth of InP on top of
SiO2/Si waveguides. By optimizing the growth conditions in terms of growth temperature and partial pressure of the
source gases with respect to the opening direction, separation and width, we show that a thin (~200 nm) layer of InP with
good morphology and crystalline quality can be grown laterally on top of SiO2. Due to the thin grown InP layer,
amplification structures on top of it can be well integrated with the underlying silicon waveguides. The proposed ELOG
technology provides a promising integration platform for hybrid InP/silicon active devices.
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