Photoluminescence of GaInAsPSbGaSb heterostructures for midinfrared radiation sources

1
Photoluminescence of GaInAsPSb/GaSb
heterostructures for mid-infrared radiation
sources

• V.M.Smirnov, P.J.Batty, A.Krier
• Physics Department, Lancaster University, UK
• V.I.Vasilev, G.S.Gagis
• Quantum-Size Heterostructures Lab, Ioffe
  Institute, Russia
•  

2
OutIine

• Advantages of 5 component alloys
• Calculation of pentanary basic physical
• characteristics
• PL characterization of 5 component
• epilayers
• Perspectives for LED and laser structures
• based on pentanaries

3
Motivation and Applications

• Molecular spectroscopy
• Ecological express-monitoring of natural and
  industrial gases
• Free space optical communications
• Medical diagnostics

Semiconductor LEDs and lasers operating at ROOM
TEMPERATURE in the 3-4 µm spectral range are
needed !!!
4

• Fundamental mechanisms, which limit the
  performance of III-V semiconductor diode lasers
  in mid-infrared wavelength range beyond 3 µm are
• inadequate electrical confinement due to
  small
• conduction and/or valence band offsets
• large non-radiative Auger recombination
  (CHHS)
•    weak optical confinement
•    lattice heating in the active region
•    interband absorption (IVBA)

5

Advantages of pentenary materials

• Ternary solid solutions (AlGaAs) have one degree
  of freedom therefore for the fixed lattice
  parameter we could not change Eg value.
• Quaternary solid solutions (GaInAsSb) have 2
  degrees of freedom
• (Eg value and lattice parameter can be chosen
  independently).
• Pentanary solid solutions (PSS) have 3 degrees of
  freedom. At fixed Eg value and lattice parameter
  we can vary any other parameter of the material,
  for example, refractive index, band offsets (for
  valence and conduction band), spin-orbit
  splitting value, etc.

In principle we can de-tune IVBA and CHHS
Auger recombination - help towards 300 K
operation
6
Isoperiodic surface to GaSb (rose) and iso-energy
surface with Eg0.3 eV (blue) in concentration
prism of PSS Ga1-xInxAsyPzSb1-y-z. Line, which
formed by the intersection of these surfaces
presents a quantity of PSS all of them are
lattice-matched to GaSb and have a bandgap
Eg0.3 eV.
Advantages of pentenary materials

Projections of lines of intersection between
isoperiodic to GaSb surface and iso-energy
surfaces on Ga-In-As-Sb composition square.  
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Advantages of pentenary materials
GaInAsPSb can be grown on four different
substrates (it is isoperiodic with GaSb, InAs,
InP and GaAs). - GaSb was used in our work
Isoperiodic surfaces with different binaries
inside the composition prism of GaInAsPSb.
8

Calculation of physical parameters using
Interpolation model
Lattice constant linear model was used based on
known binary lattice parameters
Other parameters (Eg, ?so, n, ß) non-linear
model was used based on known parameters of
binaries and bowing parameters of ternary systems
(for quaternary systems bowing parameters
assumed to be 0)
Bowing parameters taken from Vurgaftman, Meyer,
Ram-Mohan, JAP 89 (2001) 5815
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Liquid Phase Epitaxial Growth
Epitaxial growth was implemented in closed
horizontal system using slider boat. All
epilayers were grown using antimony-rich melts
Typical program for epitaxial growth of GaInAsPSb.

• Advantages
• Reduced concentration of native lattice
  defects, which are typical of GaSb and related
  solid solutions.
• Increased stability of GaSb substrate regarding
  to Ga-In-As-P-Sb liquid phase.
• Decrease of acceptor concentration in epilayer
  and increased carrier mobility
• Better reproducibility of multilayer structures.

Th-temperature of liquid phase homogenization
TL-liquid phase liquidus temperature Tg-growth
temperature (590-595 oC) ?T-the supercooling of
liquid phase (10-20 oC) tg - time of epitaxial
growth (10-30 sec)  
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Experimental results, Liquid Phase Epitaxial
Growth
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Experimental results, XRD, SEM PL
?a?2.5x10-3
XRD rocking curve for InGaAsPSb epilayer grown
on GaSb (100) with GaSb buffer layer
A - connected with impurity levels B -
band-to-band recombination
SEM image of S-891 sample surface
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Experimental Results, PL
For Ga0.03In0.97As0.81P0.06Sb0.13 Eg0.344eV (PL,
4K), 0.348eV (Varshni model, 4K), 0.321eV
(Varshni model, 300K), 0.316eV (interpolation,
300K) ?so0.285eV (interpolation, 300K)
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Activation energies
Experimental results, PL
Sample S-886-1 has the best luminescent
properties and its activation energy at high
temperatures is highest compared with the same
for InAs and InAsSb epilayers
Addition of P (phosphorous composition z
located in 0.04 z 0.1 range) increased
?SO value over bandgap parameter Eg, so a
suppression of intraband absorption of radiation
by holes takes place and the luminescence
intensity increases
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Problems connected with the creation of
mid-infrared lasers
difficult to create amplifying medium in the
semiconductor due to absorption of generated
photons at the transitions of holes from valence
band to spin-orbital split band
?so?Eg
photons with Eg energy could not be absorbed due
to transitions connected with spin-orbital
split band
?sogtEg
Experimental results pentanary vs quaternary
In the case of most GaSb based materials ? so-
Eg ? 0
But for GaInAsPSb ?so- Eg ?0.08eV (at maximum)

Luminescence intensity became higher !!!
PL spectra of Ga0.08In0.92As0.84Sb0.16/GaSb (1)
and Ga0.05In0.95As0.8P0.06Sb0.14/GaSb (2)
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Laser heterostructure (?4 µm) with injection
pumping
Active layers are GaInAsPSb, cladding (emitter)
layers are AlGaInAsSb. Band offsets values found
using interpolation model Krijn, SST 6 (1991)
27.
p-region

• Advantages of using AlGaInAsSb cladding layers
  
• wider bandgaps (with favourable positions of
  valence band top and conduction band bottom)
• small refractive indices of Al containing
  emitters (good optical confinement),
• possibility to vary the composition of active
  layer more widely

Threshold current density in such structures is
predicted to be very low at RT (V.I.Vasilev,
G.S.Gagis, G.G.Zegrya and V.I. Kuchinskii,
unpublished)
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Conclusions

• GaInAsPSb epilayers near lattice-matched to GaSb
  were grown, good surface quality confirmed by XRD
  SEM
• PL intensity for GaInAsPSb layers is higher than
  for quaternaries due to favourable band structure
• Activation energy for GaInAsPSb at high
  temperatures is highest (48 meV) among other InAs
  and GaSb based materials
• Perspective laser and LED structures for 3-4µm
  wavelength proposed

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Acknowledgements

• Authors are grateful to EPSRC for funding this
  project (grant GR/S75826/01) and for providing a
  visiting researcher support for one of us
  (V.M.S.)