Surface processing of CdTe compound semiconductor by excimer laser doping

Abstract

Laser processing technique has been developed to achieve heavy impurity doping in II–VI compound semiconductor such as CdTe which is excellent material for application in high energy flux detector because of its high absorption coefficient and energy resolution due to large atomic number and high carrier mobility. At first, transient temperature increment in CdTe due to excimer laser radiation will be discussed using computer simulation data. Using KrF excimer laser with a pulse width of 20 ns and a wavelength of 248 nm, one shot of laser of energy 80 mJ/cm 2 increases the surface temperature of CdTe more than 1000°C, the melting point of CdTe. As the laser pulse is very short and the penetration depth of UV laser light is very short, the depth of processed and modified layer is limited to few hundred angstroms. Secondly, we have experimentally studied the laser doping process for the application to detectors of high energy flux. Resistivities of CdTe surface processed by laser doping drastically decreased from 10 5 to 10 −1 Ω cm. p–i–n diode was thus fabricated on a high resistivity single crystal CdTe using excimer laser doping on one side for p-layer and n-type CdTe grown epitaxially on the other side. The p–i–n diodes resulted showed promising characteristics and high energy sensitivity. This technique is also promising to form ohmic contacts in other II–VI semiconductor devices. Because we can adapt this process at the final stages during device fabrication and also the laser effect is limited to a very thin layer, hence there will be no influence in the bulk characteristics of the device.