Route CQD
The to High-Power, Continuous-Wave, Quantum Cascade Lasers at Room Temperature
M. Razeghi, S. Slivken, J.S. Yu, K. Mi, S. Darvish, V. Yazdanpanah, A. Evans, L. Doris, J. David
Injector
Center for Quantum Devices, Dept. of Elect. and Comp. Engineering, Northwestern University, Evanston, IL 60208 Supported under ONR contract # N00014-03-1-0003 Started October, 2002 Air Force contract # F49620-03-1-0436 Started September, 2003
doping
Active Region
Injector
Ec
doping
Northwestern University
Center for Quantum Devices
Technical Approach: Laser Design
Injector Active Region
CQD
Injector
doping
Au-coated Laser Ridge
doping
Band Structure
Determine composition/ thickness of layers for each new wavelength. Used to predict emission wavelength, thermal backfilling, and continuum leakage.
Waveguide Modeling
Minimize loss due to free carrier absorption and surface plasmon coupling at each new wavelength.
Thermal Analysis
Correlate experimental and theoretical performance with actual laser geometry. Analysis of thermal stress and diode failure modes
Northwestern University
Center for Quantum Devices
Technical Approach: Material Growth and Characterization
10 m QCL w/o cap and 5 10 cladding layers 10
6
CQD
Top curve- Measured Diffraction Lower Curve- Simulation
Intensity (a.u.)
10 10 10 10 10 10
4 3 2 1 0 -1
GSMBE growth
80 K Photoluminescece peaks: 1381 nm 1393 nm Intensity (a.u.)
Wafer center 1/4 radius Halfway 3/4 radius Wafer edge
30
Structural
1E19
Donor Concentration
31 32 33 Omega/2 Theta (degrees)
Cap layer InP Cladding
1E18
InP substrate
GaInAs/AlInAs core
1200 1250 1300 1350 1400 1450 1500 Wavelength (nm)
1E17 0 Electrical 1 2 3 4 Depth (m) 5 6
Optical
Northwestern University
Center for Quantum Devices
Technical Approach: Laser Fabrication
CQD
Complex processing Mechanically weak Sensitive to defects Rectangular core Uniform stripe width
Buried ridge waveguide with electroplated Au
Ridge waveguide
Tapered core Harder to clean Uniform stripe width Simpler processing Smoother sidewalls Mechanically strong
Requires additional growth Uniform stripe width Less sidewall scattering loss Mechanically strong High thermal conductance
Double-channel waveguide
Northwestern University
Center for Quantum Devices
Technical Approach: Laser Testing and Analysis
Threshold Current Density (kA/cm )
3.5
HR coated QCLs W = 12 m
Jth = J0exp(T/T0)
20
CQD
2
T herm al Resistance (K/W )
16 14 12 10 8 1 2 3 4
3.0
2
18
Jth at 300 K (kA/cm )
HR coated QCLs W = 12 m 298 K
T0 180 150 1.0 1.5 2.0 2.5 3.0 3.5 4.0 17 -3 Doping in injector (x10 cm )
1.8 HR coated QCLs 1.6 W= 15 m 1.4 at 298 K 1.2 1.0 0.8 0.6 0.4 0.2
2.5
2.0
CW 4 mm 3 mm 2 mm 1.5 mm
Cavity Length (m m )
1.5
Pulsed 4 mm 3 mm 2 mm 1.5 mm
300 320 340 360 380 400 420 440 460 480
2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 1.5 2.0 2.5 3.0 3.5 4.0 17 -3 Doping in injector (x10 cm )
240 210
Temperature (K)
Temperature dependence
Maximum Average Power (mW/ facet) 150
Maximum CW Temperature (K)
Doping dependence
Wall-Plug Efficiency (%)
100 50 0 200 150 100 50 0 0 5 10 15 20
T= 300 K Ec= 643 meV 3 mm x 20 m pulse= 170 ns
320 Continuous QCLs, Wave =6 m 300 2 mm long, HR coated 5 m electroplated Au 280 Epilayer-up 260 240 220 200 180 160 50 45 40 35 30 25 20 15 10 5 Ridge Width (m)
L= 3 mm L= 4 mm
L= 2 mm
T= 300 K Ec= 736 meV 3 mm x 25 m pulse= 170 ns
CW operaton
0.8 1.0 1.2 1.4 Current (A) 1.6 1.8
0.0
25
30
35
Duty Cycle (%)
Heterostructure dependence
Geometry dependence
Northwestern University
Center for Quantum Devices
6 m Laser Measurements Done at NRL
CQD
CQD
2.0
CW = 6 m
15
Wallplug Efficiency (%)
T = 100 K 150 K 200 K
CW = 6 m
T = 100 K 150 K
1.5
Power ( W )
10
200 K 250 K
1.0
250 K 295 K 300 K
5
295 K
0.5
0.0 0.0
0.5
1.0
1.5
0 0.0
0.5
1.0
1.5
Injection Current (A)
Injection Current (A)
CW Pout > 1.1 W @ 200 K, 640 mW @ 295 K, wall(295K) = 4.5%
Northwestern University
Center for Quantum Devices
Highest Average Power, Room Temperature, Diodes at = 4.08 m
Ga0.326In0.674As/ Al0.61In0.39As Ec~770 meV
Average Power (mW) 250 W= 13.5 m, L= 3 mm 200 150 100 50 0
T= 298 K = 4.08 m
CQD
Coated Uncoated
170 ns pulses
3x1017 cm-3
3x1017 cm-3
T= 300 K W= 13.5 m, L= 3 mm = 4.084 m
Intensity (a.u.)
0
10
20 30 40 Duty Cycle (%)
50
60
300 K Jth of 1.6 kA/cm2 for coated, 3 mm cavity
3.4 3.6 3.8 4.0 4.2 4.4 4.6
>200 mW output power at 25% duty cycle
Wavelength (m)
Northwestern University
Center for Quantum Devices
4.3 m Laser Measurements Done at NRL
CQD
CQD
1.25 1.00 0.75 0.50 0.25
280 K
10
Output Power (W)
CW = 4.3 m
Wallplug Efficiency (%)
T = 100 K 160 K 200 K
8 6 4 2
CW = 4.3 m
T = 100 K 160 K 200 K
240 K
240 K
280 K
0.00 0.0
0.2
0.4
0.6
0.8
1.0
0 0.0
0.2
0.4
0.6
0.8
1.0
Current (A)
Current (A)
CW @ 160 K: Pout 1 W, wall = 8.1%
Northwestern University
Center for Quantum Devices
Summary of Laser Results
Jth Average Peak (kA/cm2) Power (W) Power (mW) Continuous Power (mW) @ 300 K @ 300 K @ 300 K 1.6 1.2 1.68 1...