Si-based Towards Quantum cascade lasers: Achievements and Challenges
Paul Scherrer Institute, Switzerland University Neuchatel, Switzerland CNRS-LPN, France STMicroelectronics, France H. Sigg, A. Borak, S. Tsujino, L. Diehl*, C.V. Falub, M. Scheinert, E. Mller, D. Grtzmacher J. Faist U. Gennser Y. Campidelli, O. Kermarrec, D. Bensahel
*present address: Harvard University, USA
Motivation: bring opto to Si micro electronics Distinction: 0 / 100 approach and not 100 / 100!
01/2004
1
Strain Symmetrization / Fundamentals B
lattice mismatch between Si and Ge is 4% strain symmetriesed structures on relaxed (pseudo) substrate is required
Many defects 7 Low temperature growth 300 C ( MBE) 7 Our investigations:
CM-polished surface --------------------SiGe capping layer (50% Ge) --------------------Relaxed buffer (0- 50 % Ge) ----------------------
Quality of growth 7 Processing 7 Bandstructure Parameters 7 transport properties (linewidth, free carrier
absorption, etc.) 7
Si (100) substrate
1m
Parasitic current transport via LH bands 7 Leakage currents 7 QC design 7 Emission Efficency 7
? Figure of merit for laser ?
01/2004
2
Benchmark Si/SiGe cascade emitter
/ Fundamentals B
Design
Strain compensated structure 4 Active region based on bound-to-continuum transition 4 Wide HH miniband 4 Interdispersed LH band 7
Si0.2Ge0.8
HRTEM
XRD (004)
Growth
LT MBE growth (320 C) 4
30 periods
Excellent run by run reproducibility 4 No noticable increase of interface roughness as period number is increased 4 Roughness 0.6 nm 7 WG fabrication 4
64 66 68 2Theta [2 deg] 70 72
15 periods
3 periods
60
62
01/2004
3
Figure of Merit
Material Gain
gpeak
Material Loss (cladding, injector)
fosc m* GFWHM-1 Dninv Dninv j/e t
N3D m* / (w2t)
amat
Loss Waveguide (contact) aWG
Gcont s0 / (w2t2) ssquare / (wtl)2 G=Wmode/l; s0 = ssquare/l
01/2004
4
Linewidth (QW)
Good agreement between experiment and k.p calculation assuming 30 meV lifetime broadening 4 (APL, L. Diehl et.al.) But nature of broadening yet unknown 7 ITQW2003 S. Tsujino et.al.
01/2004
5
Coupled Quantum Wells
L. Diehl et.al. to be published
01/2004
6
Current in Cascade structure
Front and back contacts
30 m x 2400 m
severe contact serial problem resistances 7 no current limitations yet (< 7 kA/cm2) of injector 4
+
4.5 4.0 3.5 3.0
(1.4 kA/cm2) J014 (15periode)
more experiments needed 7
10um 3um
-
Bias (V)
2.5 2.0 1.5 1.0 0.5 0.0 -1000 0 1000 2000 3000 4000 5000 6000 7000
2 Current Density (A/cm )
01/2004
7
Resonant tunneling structure
B
low leakage currents at T 77 K 4 resonant current 1 kA/cm2 @ 103 kV/cm, 40 barrier 1/10 of WKB approach 7 coupling strength? Level anti-crossing observed 4
applied voltage
tunneling through LHSO1 not observed conservation of hole character 4 supported by Magneto-tunneling experiments possibility of low injection losses of HHs into LH continuum. 4
U.Gennser FTM-workshop, Cosica 2003
01/2004
8
Achievements/Challenges
Estimations
Parameters &w (meV)
Achievements
Challenges
180 45 5 100 <3 40 1.5 ~3 1.5 1017 0.2 15 1/100W 60 1 (G~ 5%) 1019
60
ditto 30 >> 10 500 > 30 ditto > 15
Ultimate limit? for nup/lper ~ <N>
Gain
gpeak
r f m e 1 n up - n d 2 m * C l per )1.8 $ 10 - 14 cm 2 meV
GFWHM (meV) j (kA/cm2) tup (fs) nup (109cm-2) lper (nm) gpeak (cm )
-1
Loss material (cladding, injector)
wt
me 1 m * &~ 2 x N inj )1.8 $ 10 - 14 cm 2 meV
<N>inj(cm-3) m*/me amat (cm-1) ssquare
g peak '~ a mat K C $ ~x + 10f15
(III - V): a
amat
Loss Waveguide (contact)
g peak
ma...