The results of first principles band structure calculations are incorporated into a many-body laser theory to investigate strain and quantum confinement effects in group-III nitride lasers

Chow, W. W.

Hughes, S.

Knorr, A.

Koch, S. W.

Nelson, J. S.

Wright, A. F.

UNT Digital Library

Microscopic Theory of Gain in a Group-I11 Nitride _, < .  . -  A I  Strained Quantum Well Laser -,/+,- La !  L Lii’ JjL 2 2 iu,s 0o.u  y-o W. W. Chow, A. F. Wright and J. S. Nelson Sandia National Laboratories Albuquerque, NM 87185-0601 Tel: (505)844-9088 S. Hughes, A. Knorr and S. W. Koch Department of Physics and Materials Sciences Center Philipps-University 35032 Marburg;’ Germany Abstract The results of first-principles band structure calculations are incorporated into a many-body laser theory to investigate strain and quantum confinement effects in group-I11 nitride lasers. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completen-ess, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, r w m -  mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. ~~ ~~ ~~ ~ DISCLAlMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document . W. W. Chow et al., Microscopic Theory-.. Microscopic Theory of Gain in a Group-I11 Nitride Strained Quantum Well Laser W. W. Chow, A. F. Wright and J. S. Nelson Sandia National Laboratories Albuquerque, NM 87185-0601 S. Hughes, A. Knorr and S. MT. Koch Department of Physics and Materials Sciences Center Philipps-University 35032 Marburg, Gerrnany 1 The study of gain properties in group-I11 nitride quantum wells is com- plicated by the incomplete knowledge of band structure properties, and the need for a consistent treatment of strong many-body Coulomb effects. Varia- tions in material quality hamper experiments for investigating band structure properties. As a result, some important material parameters are unhown and much discrepancies exist in others. The strong Coulomb interactions due to high exciton binding energies make it necessary to properly account for the many-body electron-hole effects. The microscopic high-density plasma gain model [l] , which is used successfully in infrared 111-V lasers [2], may be insufficient because it  treats the interband Coulomb interactions as a pertur- .. W. W. Chow et d., Microscopic Theory ... 2 bation, and accounts only for incoherent polarization decay. This paper describes an approach that involves a first-principles band structure calculation, the results of which are incorporated into a microscopic laser theory. The band structure calculation applies a densify-functional method based on ab initio pseudopotentials and plane-wave expansions [3]- This method provides a single analytical model for computing the group- I11 nitride material properties, thus ensuring consistency in the values for the different band structure parameters , and circumventing the discrepan- cies present in the literature due to different experimental conditions, or different computational methods. Having a complete set of the relevant ma- terial parameters allows us to investigate the effects of strain and quantum confinement, in structures such as InGaNIGaN and InGaNIAlInN (Fig. 1). The quantum well gain is computed by numerically integrating the semi- conductor-Bloch equations [l], thereby treating exactly the Hartree-Fock con- tributions, in particular, that describing the interband Coulomb interactions. 1 Carrier-carrier scattering, resulting in carrier thermalization and polarization dephasing, significantly affects the laser gain. Both effects are treated at the level of the quantum kinetic equations in the Markov limit. This approach circumvents the usual introduction of the phenomenological dephasing time, Tz, whose applicability for wide band gap lasers is still under investigation. Figure 2 shows an esample for the calculated dephasing rates. - W. W. Chow et al., Microscopic Theo ry.... - 3 Our theory predicts that the differences in bandstructure properties, and the significantly stronger Coulomb effects lead to gain properties in nitride- based lasers that are different than those in infrared 111-V lasers. The gain peaks are located at lower energies than the exciton resonance, and an absorp- tion resonance remains even at carrier densities that are sufficiently high for gain to occur. Both phenomena are observed in the 11-VI lasers (which also have high exciton binding energies)] and are indications of strong Coulomb interactions. Specific results involving InGaN/GaN, GaAs/A.lGaN and In- GaN/AlhN quantum wells will be presented] e.g., the polarization depen- dence of the laser gain as a function of strain (Fig. 3). Finally, the detailed treatment of the physical mechanisms contributing to laser gain allows us to develop a gain model, that contains the proper balance between rigor and simplicity, for use in parametric studies of laser configurations. Details of this model and its range of validity will be dis- cussed. This work is supported by the U.S. Department of Energy through con- tract No. DEAC04-94AL85000, the Army Research Office under contract No. DAAH04-95-C-0008, and the Deutsche Forschungsgemeinschaft. W. W. Chow et d., Microscopic Theo ry.... 4 References H. Haug and S. W. Koch, Quantum Thwry of the Optical and Electronic Properties of Semiconductors, 3rd ed. (World Scientific, Singapore, 1994) - W. W. Chow, S. W. Koch and M. Sargent 111, Semiconductor-her Physics (Springer Verlag, Berlin, 1994) Chaps. 5 and 6. A. F. Wright and J. S. Nelson, Phys. Rev. B 51, 7866, 1995. W. W. Chow et al., Microscopic Theory-.. 5 Figure Captions Fig. 1. Computed valence bands near the I?-point for unstrained GaN (solid curves) and GaN strained to fit on AZ~.XGUO.~~N (dashed curves). These results are used to obtain the hole effective masses and the deformation po- tentials. Fig. 2. Computed scattering rate for electrons (solid curve) and holes (dashed curve) in a GaN/AlGaN quantum well. The carrier density is 3 x 1012m-2, IC is the carrier moment, and a, is the 2-dimensional exciton Bohr radius. Fig. 3. TE and TM peak gain versus carrier density for different strain in the quantum well. The laser structure is 6nm GaN/AZl-,In,N with E =(a) 0.13, (b) 0.21 and (c) 0.30. d- b 0 7 b 0 (AH) A6~au3 0 cr) 0 0 U a, S a c/) S 3 .- 1 4-J d- 0 01 I E z a, 0 

Microscopic theory of gain in a group-III nitride strained quantum well laser

https://digital.library.unt.edu/ark:/67531/metadc670682/m2/1/high_res_d/266778.pdf

Microscopic theory of gain in a group-III nitride strained quantum well laser

Abstract

Similar works

Full text

Available Versions

UNT Digital Library