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Publication Date: 2015-Feb-21
Document File: 9 page(s) / 82K

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Methods To remove Heat From Semiconductor Laser Gain Chip


The wall-plug efficiency of quantum cascade lasers and other types of semiconductor lasers is typically very low.  Heat generated by excess power supplied to a laser gain chip should be removed efficiently to ensure proper operation conditions of the laser gain chip.  The laser gain chip may be mounted on a heat spreader (or submount) made of metal, alloys, ceramics, or other materials.  The heat spreader in turn may be mounted on heat removal devices such as thermal electric coolers. 

The laser active region (the gain region) of a laser gain chip is typically fabricated using epitaxial growth method(s) to deposit desired materials on a semiconductor substrate.  Thus, the laser active region is usually on one of the surfaces of the substrate.  In some cases the laser active region may be buried (shallowly) inside the substrate. 

Figures 1(a) and 1(b) illustrate two common methods of mounting a laser gain chip on a heat spreader.  In the active side up mounting method shown in Figure 1(a), laser substrate 2 is mounted on heat spreader 3, and laser active region 1 is “upwards” on laser substrate 2.  Heat spreader 3 is in turn mounted on heat removal device 4 which may be a thermal electric cooler (TEC) or other type of heat removal device.  The advantage of this method is its simplicity and high yield.  In the active side down mounting method shown in Figure 1(b), laser active region 1 is in contrast mounted “downwards” on heat spreader 3.  Optionally, a buffering layer (or multi-layers) of buffering material(s) 5 may be disposed between laser active region 1 and heat spreader 3.  The advantage of this method is that laser active region 1 is closer to heat spreader 3, improving heat removal efficiency.  On the other hand, because laser active region 1 is typically very fragile, this mounting method is more difficult to implement. 


According to the present disclosure, improved cooling methods are provided to remove heat from the laser gain chip, from both the active side and the substrate side of the device.    

Figure 2 illustrates an embodiment wherein laser active region 1 is mounted between two heat spreaders 3.  Laser active region 1 is mounted “downwards” on lower heat spreader 3.  Upper heat spreader 3 is mounted on the other side of laser substrate 2.  Heat spreaders 3 are mounted to respective heat removal devices 4, which may be thermal electric coolers (TECs) or other heat removal devices.  Optionally, a layer (or multi-layers) of buffering material(s) 5 may be disposed between laser active region 1 and lower heat spreader 3.     

One of the difficulties of implementing this method is the thermally induced stress on the laser gain chip, especially when the laser works in a pulsed mode.  The thermally induced stress originates in the mismatch of the thermal expansion coefficients of the various materials.  If this st...