Semiconductors laser etching

As in any other laser, the lasing threshold in a semiconductor laser diode is reached when the gain of the active material overcomes the losses of the laser cavity. These losses have two basic origins, namely the finite reflectivity of the mirrors mid distributed losses due to scattering and parasitic absorption in the active medium. In contrast to other lasers, the mirrors in typical semiconductor lasers are simply formed by cleaved or etched crystal facets. Therefore, the reflectivity (Fresnel reflectivity) is rather low, about 20% in the case of the nitrides. 

Figure 18. Schematic diagram of the illumination of a surface in laser light-Semiconductor sensitive etching.

Compound Semiconductors, Electrochemical Decomposition, Fig. 3 Etch pits caused by galvanic corrosion in a p-InP-based semiconductor laser (From... 

Osgood, R.M., Sanchez-Rubio, A., Ehrlich, D.J., and Daneu, V., Localized laser etching of compound semiconductors in aqueous solution. Appl. Phys. Lett. 40 391-393(1982)... 

Fig. 12. Schematic of surface-emitting laser diodes where U represents the active region (a) planar cavity surface-emitting laser diode (PCSEL) with 45° etched reflectors and (b) vertical cavity surface-emitting laser diode (VCSEL) with semiconductor-based multilayer mirror stacks grown into the stmcture.

The capability to control an excimer laser beam also is exploited in the semiconductor industry, where these lasers are used to etch elaborate features during the fabrication of semiconductor chips. Neil Bartlett probably never dreamed that his explorations of the chemistry of xenon would lead to such exotic applications. 

The second area of activity also includes some problems in laser electrochemistry of semiconductors, which are in no way confined to the above-considered light-sensitive etching. First of all, it is threshold electrochemical reactions stimulated by intensive laser radiation. Such reactions may proceed via new routes, because both highly excited solution... 

Finally, surface analysis has been used in the investigation of metal silicides used to form rectifying Schottky barrier contacts to semiconductors. These silicides are formed by thermal or laser sintering of the metal after deposition onto the substrate. Excess unreacted metal is removed by chemical etching. XPS has been used to show that the metal has been oxidized if the excess metal cannot be removed (52). 

---