Thermal analysis of laser diode on different types of submount

The substrate removed laser can be mounted on different materials by van der Waals forces. The 2-D temperature profile of a LD transfer-bonded to 10-m-thick submounts (180-m-wide) composed of alumina, GaAs, and Si was evaluated. The

Figure 5.8 Simulated temperature distribution of a transfer-bonded thin-film laser on 10 m thick submount ((a) alumina, (b) GaAs, and (c) Si at 40 mW heat load at room temperature T0=20C by FEM model. A perfect heat sink is

assumed on the bottom face.

x-coordinate (m) y -co o rd in ate (  m) y -co o rd in ate (  m) y -co o rd in ate (  m)

Page | 140 alumina (aluminium oxide) thermal properties are in line with those formed by sputtering where voids and other inclusions may be present. The thermal interface between the submount and device is assumed to be perfect. The bottom surface of submount is fixed at room temperature (T0 = 20C). The top surface and the surface on each side of both the LD and the submount are assumed to be thermally isolated. Fig. 5.8a shows the 2-D temperature profile of the transfer-bonded laser on an alumina submount. Due to the low thermal conductivity of alumina, the heat spreads laterally resulting in a high junction temperature of 48.2°C. In Fig. 5.8b, the LD on GaAs shows a more obvious broad parabolic heat spreading from the ridge region. The thermal distribution profile of LD on Si as seen in Fig. 5.8c that shows a parabolic heat spreading and the lowest temperature rise at the junction.

Figure 5.9 Simulated temperature at the junction of a transfer-bonded thin-film laser with 40 mW heat load at room temperature (T0=20C) as a function of submount

thickness composed of alumina, GaAs and Si respectively.

Fig. 5.9 shows the calculated junction temperature of the LD as a function of submount thickness for different submount materials. It shows that the junction temperature of a transfer-bonded laser on alumina strongly depends on its thickness, while it is relatively independent of thickness for GaAs and Si. Thus, thickness of alumina should be minimised to reduce the heat conduction path between the ridge region and the heat sink.

0 10 20 30 40 50 20 30 40 50 60 70 80 90 100 110 submount thickness(m) Ma x. t e mp e ra tu re a t ju n ct io n T ma x (  C) Alumina GaAs Si Transfer-bonded laser on a perfect metal heat sink

Page | 141

5.5 Conclusions

The 2-D temperature distribution of an AlGaAs/GaAs MQW LD with a 3-m-wide ridge with 40 mW of power dissipated was modelled by FEM software for different cavity lengths and device configurations. The total thermal resistance was calculated by the FEM model and by an analytical model. The FEM model shows a reasonable matching with measured thermal resistance of LD. It is essential to reduce the thermal resistance for a 200-m-long cavity laser due to the high heat power density. This can be done by increasing the p-metal layer thickness in order to increase the lateral heat spreading. The heat flow from the heat source is dominated by the downward heat flow to the heat sink and the contribution from the upward heat flow is minimal. Comparing the simulated maximum temperature (Tmax) of the junction in the transfer-bonded LD on different submount materials (e.g. GaAs, alumina and Si), shows that reducing the alumina thickness is critical to decrease the junction temperature of the device. Both GaAs and Si submounts show a weak dependence of the junction temperature on thickness. For a 10-m-thick submount, Si provides the lowest Tmax of about 22.2C for 40 mW of power dissipation.

5.6 References

[1] T. Amano, S. Ukita, L. Ma, et al, “Thermal Conductive Properties of a Semiconductor Laser on a Polymer Interposer”, Jpn. J. Appl. Phys., vol. 52, no. 4s, pp. 04CG05, Mar. 2013.

[2] B. Corbett, C. Bower, A. Fecioru, et al, “Strategies for integration of lasers on silicon”, Semicond. Sci. Technol., vol. 28, no. 9, pp.1-6, Aug. 2013.

[3] R. Saeidpourazar, M. Sangid, J. Rogers, et al, “A prototype printer for laser driven micro-transfer printing”, Journal of Manufacturing Processes, vol. 14, no. 14, pp. 416–424, Oct. 2012.

[4] R. H. Kim, D. H. Kim, J. Xiao, et al, “Waterproof AlInGaP optoelectronics on stretchable substrates with applications in biomedicine and robotics”, Nature Materials, vol. 9, no. 11, pp. 929–937, Oct. 2010.

[5] J. Yoon, A. J. Baca, S. I. Park, et al.: 'Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs', Nature Materials, vol. 7, no. 11, pp. 907–915, Jan. 2008.

[6] X. Sheng, C. Robert, S. Wang, G. Pakeltis, B. Corbett, J. A. Rogers, “Transfer printing of fully formed thin-film micro-scale GaAs lasers on silicon with a

Page | 142 thermally conductive interface material,” Laser & photonics reviews, vol. 9, no. 4, pp. L17-L22, July. 2015.

[7] H. Yi, J. Diaz, I. Eliasheevich, et al, “Temperature dependence of threshold current density Jth and differential efficiency ηd of high-power InGaAsP/GaAs

(λ=0.8 m) lasers,” Appl. Phys. Lett., vol. 66, vol. 3, pp. 253–255, Jan. 1995.

[8] H. K. Choi, G. W. Turner, 'Mid-infrared semiconductor lasers based on antimonide compounds,' in Manasreh, M. O. (Ed.): “Optoelectronic properties of Semiconductors and Superlattices”, (Press, 1997), pp. 369–433.

[9] V. P. Gribkovskii, “Injection lasers,” Prog. Quant. Electr., vol. 19, no. 1, pp. 41- 88, 1995.

[10] L. A. Colden, and S. W. Corzine, 'Diode Lasers and Photonic Integrated Circuits' (John Wiley, 1995, 1st edn.)

[11] X. S. Liu, H. M. Hu, C. G. Caneau, et al, “Thermal Management Strategies for High Power Semiconductor Pump Lasers,” IEEE Transactions on components and

packaging technologies, vol. 29, no. 2, pp. 268–276, Jun. 2006.

[12] V. V. Bezotosnyi, O. N. Krokhin, V. A. Oleshchenko, V. F. Pevtsov, Yu. M. Po pov, E. A. Cheshev, “Thermal modeling of high-power laser diodes mounted using various types of submounts,” Quant. Electr., vol. 44, no. 10, pp. 899-902, May. 2014. [13] W. B. Joyce, R. W. Dixon, et al, “Thermal resistance of heterostrucutre lasers”,

J. Appl. Phys., vol. 6, no. 2, pp. 855–862, 1975.

[14] J. P. Fu, R. G. Yang, G. Chen, et al, “Integrated electroplated heat spreaders for high power semiconductor lasers,” J. Appl. Phys., vol. 104, no. 6, pp. 4907–4911, 2008.

[15] H. S. Carslaw, and J. C. Jaeger, “Conduction of Heat in Solids” (Oxford University Press, 1959, 2nd edn. 1960)

[16] J. Piprek, “Semiconductor optoelectronic devices: Introduction to Physics and Simulation” (Academic Press, 2003, 1st edn.)

[17] http://www.ioffe.ru/SVA/NSM/Semicond/GaAs/thermal.html

[18] Y. S. Touloukian, R. W. Powell, C. Y. Ho, and P. G. Klemens, “Thermal Conductivity,” TPRC Data Series, vol. 2, Plenum, New York, 1970.

[19] T. M. Tritt, “Thermal conductivity: Theory, Properties, and Applications,” (Springer Science & Business Media, Berlin, 2005)

[20] S. Sze, “Physics of Semiconductor Devices”, (Wiley, New York, 1981, 2nd edn.) [21] L. M. JiJi, “Heat conduction”(Springer. Verlag Berlin Heidelberg, 2009, 3rd edn.) [22] J. N. Reddy, “An Introduction to the Finite Element Method”, (McGraw-Hill, 2006, 3rd edn.)

Page | 143