Short wavelength and strain compensated InGaAs-AlAsSb. AlAsSb quantum cascade lasers. D.Revin, S.Zhang, J.Cockburn, L.Wilson, S.

Transcription

1 Short wavelength and strain compensated InGaAs-AlAsSb AlAsSb quantum cascade lasers D.Revin, S.Zhang, J.Cockburn, L.Wilson, S.Menzel, Department of Physics and Astronomy, University of Sheffield, United Kingdom M.Steer, A.Krysa, M.Hopkinson, R.Airey EPSRC National Centre for III-V Technologies, University of Sheffield, United Kingdom

2 Outline 1. Motivation, design requirements and material systems for λ 3-5 µm QCLs 2. Short wavelength In 0.53 Ga 0.47 As/AlAs 0.56 Sb 0.44 QCLs lattice matched to InP 3. Strain compensated InGaAs/AlAsSb QCLs 4. Improved performance of strain compensated InGaAs/AlAsSb(AlAs) QCLs

3 1. Motivation Gas sensing applications in λ 3-5 µm range medicine (breath analysis) military (countermeasures) exploring of minerals We concentrate on λ 3.34 µm for ethane sensing in less explored λ < 4 µm range for quantum cascade lasers

4 1. Design requirements and material systems for short wavelength λ ~ 3 5 µm QCLs Primary requirement: quantum wells must be deep enough 2500 Barrier heights ~2.1eV InAs/AlSb ~1.6eV Energy (mev) E3 E2 3 µm transition energy 390meV 520meV 740meV Distance(A) For λ 3µm design: E3-E2 ~420 mev GaAs- AlGaAs (GaAs) InGaAs- AlInAs lattice matched (InP) InGaAs- AlInAs strain compens. (InP) InGaAs- AlAsSb (InP) InAs- AlSb (InAs) Upper laser level (E3) energy ~ 700 mev focus of our research with well established InP technology

5 1. Wavelength: how low can we go in InGaAs/AlAsSb system? λ=3µm places E3 (~700meV) above the satellite valley in lattice matched InGaAs/AlAsSb system AlSb AlSb AlAs 0.56 Sb 0.44 AlAs 0.56 Sb 0.44 Will intervalley scattering stop the lasing below λ ~ 3.7 µm? Al 0.6 In 0.4 As E L ~620meV Γ L Al 0.6 In 0.4 As Γ E C ~0.74eV X X, L E C ~1.6eV X E L ~520meV X L X E C ~2.1eV E L ~750meV In 0.7 Ga 0.3 As In 0.53 Ga 0.47 As (a) (b) (c) InGaAs/AlInAs/InP (strain compens.) InGaAs/AlAsSb/InP InAs InAs/AlSb

6 2. Short wavelength InGaAs/AlAsSb QCLs lattice matched to InP M3255, λ ~ 3.5 µm laser Band profiles M3253, λ ~ 3.05 µm laser Energy (ev) X- valley Energy (ev) X- valley -0.4 F=100kV/cm λ~3.5µm -0.4 F=128kV/cm λ~3.1µm Position (nm) Position (nm) Upper laser levels are calculated to be higher by ~ 30 and ~ 120 mev than the minimum of the satellite valley in In 0.53 Ga 0.47 As lattice matched to InP

7 2. Short wavelength InGaAs/AlAsSb QCLs lattice matched to InP Ridge size: 25µm x 1.5mm no HR coating Normalized intensity (a.u.) M K 80K M3255 J th (ka/cm 2 ) 300K M3253 M3255 T 0 =130K Temperature (K) Wavelength (µm) λ~3.05 µm is the shortest wavelength for InGaAs/AlAsSb/InP QCLs (Revin et al. APL, 90, (2007)

8 2. Short wavelength InGaAs/AlAsSb QCLs lattice matched to InP room temperature, λ ~ 3.6 µm laser only low-temperature, λ ~ 3.05 µm Voltage (V) K Current density (ka/cm 2 ) 80K 120K 160K 180K 200K 220K 240K 260K 280K 300K Peak optical power (mw) Voltage (V) K 80K 60K 80K 100K Current density (ka/cm 2 ) 110K Peak optical power (mw) There is possibly strong influence from intervalley scattering but it does not stop the lasing!

9 3. Strain compensated InGaAs/AlAsSb QCLs on InP How to reduce the intervalley scattering? Energy (ev) X valley L valley Γ valley X in In x Ga 1-x As Calculations are based on Vurgaftman et al, JAP. 89, (2001) Energy separation (mev) Γ-X separation strain Γ-L separation X in In x Ga 1-x As lattice matched to InP The use of higher indium composition should help in increasing the effective (free from intervalley scattering) depth of InGaAs QWs

10 3. Strain compensated InGaAs/AlAsSb QCLs on InP Identical design: In 0.53 Ga 0.47 As/AlAs 0.56 Sb 0.44 In 0.6 Ga 0.4 As/AlAs 0.67 Sb 0.33 In 0.7 Ga 0.3 As/AlAs 0.78 Sb M3254 (reference) - M3259 (strain compensated) - M3257 (strain compensated) 0.2 L-valley for 70% strain compensated Energy (ev) X-valley for lattice matched F=92kV/cm λ~4.05µm Distance (nm)

11 3. Strain compensated InGaAs/AlAsSb test superlattices Sb fraction has to be adjusted to give the best compensation of the strain X-rays diffraction has been used to assess - quality, - thickness and - remaining strain in the strain compensated InGaAs/AlAsSb test superlattices with periods similar as in the injectors Intensity (a.u.) 10 7 superlattice InP substrate Λ=3.6 nm Omega/2Theta (sec) 100 periods In 0.67 Ga 0.33 As - 22 Å (~ 8 MLs) AlAs 0.76 Sb 0.24 (?) - 13 Å (~ 4 MLs)

12 3. Feasibility of strain compensated InGaAs/AlAsSb QCLs on InP Voltage (V) λ~4-4.3µm In 0.7 Ga 0.3 As/AlAs 0.78 Sb T=80K T=295K 140K 160K 180K 200K 220K 240K 260K 280K 300K 320K Current density (ka/cm 2 ) Peak optical power (W) J th (ka/cm 2 ) In 0.53 Ga 0.47 As/AlAs 0.56 Sb M3254 In 0.6 Ga 0.4 As/AlAsSb - M3259 In 0.7 Ga 0.3 As/AlAsSb - M3257 fitting for T 0 =150K Temperature (K) No degradation for strain compensated QCLs with the performance similar to the lattice matched QCLs (Revin et al. APL, 90, (2007)

13 3. Strain compensated InGaAs/AlAsSb QCLs on InP Details of the design and performance Wafer number M3254 M3259 M3257 Indium concentration in InGaAs quantum wells (%) Position of the lowest satellite valley in InGaAs quantum wells (mev) Energy between upper laser level and the lowest satellite valley in InGaAs quantum wells (mev) Calculated wavelength (µm) Wavelength of the laser emission for T = 80 / 300 K (µm) 4.1/ /4.4 4/4.3 FWHM of EL peak for T = 80 / 300 K (mev) 40/73 44/68 42/72 Average J th for T = 80 / 300 K (ka/cm 2) 3.4/ / /10.9 Maximum pulsed optical power at J ~ 15kA/cm 2 for T = 80 / 300 K (W) 0.8/ / /0.12 Characteristic temperature T 0 (K)

14 4. Strain compensated InGaAs/AlAsSb QCLs with AlAs barriers Further improvement of QCL performance Identical design: In 0.6 Ga 0.4 As/AlAsSb(AlAs) - M3260 (wafer A) In 0.6 Ga 0.4 As/AlAsSb - M3259 (wafer B) AlAs 1.0 AlAs AlAs barriers in the active region (~3 MLs) should help to reduce interdiffusion of Sb at InGaAs/AlAsSb interfaces in the active regions Energy (ev) F=90kV/cm λ~4.25µm injector X-valley Distance (nm)

15 4. Strain compensated InGaAs/AlAsSb QCLs with AlAs barriers For QCLs with AlAs barriers High energy shift and narrower EL peaks - InGaAs QWs are clear from Sb and have better profile - better interface quality (?) Normalized intensity (a.u.) Wavelength (µm) T = 80K T = 295K CO 2 EL EL AlAs barriers AlAsSb barriers Energy (mev) Laser and electroluminescence spectra

16 4. Strain compensated InGaAs/AlAsSb QCLs with AlAs barriers J th (ka/cm 2 ) wafer A (with AlAs barriers) wafer B T 0 =180K Temperature (K) T 0 =130K Voltage (V) 14 wafer A (with AlAs barriers) 160K 180K T=295K Current density (ka/cm 2 ) 200K 220K 240K 260K 280K 300K 320K Peak optical power (W) Improved performance for the QCLs with AlAs barriers : - lower threshold - by factor more than 2, - higher optical power W at 300K compared with 0.15 W for wafer B (Revin et al. APL, 91, (2007)

17 Conclusions 1. First In 0.53 Ga 0.47 As/AlAs 0.56 Sb 0.44 QCLs lattice matched to InP working down to 3.05 µm 2. First strain compensated InGaAs/AlAsSb QCLs 3. Improved performance of InGaAs/AlAsSb QCLs with AlAs barriers in the active regions 4. Expected room temperature operation for the strain compensated QCLs down to λ ~ µm Acknowledgements: