Intersubband Transition ISBT in Quantum Well

1
Quantum well intermixing for photonic device
integration
Motivation
Modification of bandgap energy without extra
epitaxy
Modification of lasing wavelength of QW
laser Monolithic Integration of photonic and
optoelectronic devices by area-selective
bandgap control
Modification of refractive index and electrical
conductivity without complicated device
processing
Absorption coefficient change of waveguide
and photodetector Improvement of optical
wave confinement Improvement of lateral
current confinement (by Ion implantation
enhanced, impurity induced)
Kwangju Institute of Science Technology(K-JIST)
2
Concept of the relative bandgap positions in
photonic integrated circuits
Waveguide should be transparent to the
laser wavelength ? Eg (laser) lt Eg (waveguide)
Modulator red-shifted by electric field ?
Eg (laser) lt Eg (modulator)
Absorption
Modulator
Waveguide
Detector should absorb the laser wavelength
? Eg (detector) lt Eg (laser)
Detector
Laser
Bandgap energy (eV)
Eg (detector) lt Eg (laser) ? Eg (modulator) lt Eg
(waveguide)
Kwangju Institute of Science Technology(K-JIST)
3
Principle of quantum well intermixing (QWI)
As-grown
After QW intermixing
QW inherently metastable (large concentration
gradient of atomic species across the
well/barrier interfaces)
High temperature annealing
Laser irradiation (CW, pulse)
Impurities, ions
E
E
g'
g
Point defects (or vacancies)
Square well
E
gt E
Parabolic-like shape
g


g
IFVD
No impurities or defects
Dielecric capping layer
Interdiffusion of atom species consisting of QWs
QWI
blue shift of bandgap wavelength
Kwangju Institute of Science Technology(K-JIST)
4
Impurity-free vacancy disordering (IFVD)
Parameters influencing IFVD
Kinds of material (SiOx, SiNx, SrF2, GaO3,
PSiO2, etc.), Stoichiometry of dielectric
films, Deposition parameters, Deposition technique
2. Properties of dielectric capping layer
3. Annealing condition
Dielectric capping layer
Annealing environment (Vacuum, N2, air, Ar etc.)
1. Structural parameters
Annealing parameters
(RTA temperature, time)
Intermediate semiconductor cap layers, Distance
between surface and QWs, No. of QW, thickness
and composition of QW
III-V QW heterostructure
Kwangju Institute of Science Technology(K-JIST)
5
IFVD of InGaAs/InP MQW structure Influence of
InGaAs cap layer and stoichiometry of dielectric
capping layer
? Different hybrid capping layers ? PL
measurements - At room temperature -
After removing dielectric layers ? With/without
InGaAs cap layer SiO2 cap layer induces
much larger blueshift than Si3N4 cap layer ?
With InGaAs cap layer - SiOx highly enhances
QWI - SiNx dont enhance QWI
Results
Blueshift of 117 meV
SiOx
InGaAs
RTA time 25 sec
InGaAs
SiNx
N2O 800 sccm for SiOx, NH3 30 sccm for SiNx
Kwangju Institute of Science Technology(K-JIST)
6
IFVD of InGaAs/GaAs MQW structure Influence of
stoichiometry of dielectric capping layer
Results
Si vacancy act as the path for the
cation vacancy indiffusion
? Magnitude of the blue shift increases with the
decrease of SiH4 flow rate for SiOx and SiNx
capping layer - Increased porosity of
dielectric capping layers ? SiOx capping layer
induces larger blueshift than SiNx capping layer
Kwangju Institute of Science Technology(K-JIST)
7
Application of IFVD Multiwavelength InGaAs/GaAs
LD for photonic integrated device
Kwangju Institute of Science Technology(K-JIST)