n-and p-type doping of CdTe grown heteroepitaxially on GaAs substrate by radical assisted metal organic chemical vapor deposition technique were studied. n-type doping was studied by the gas phase n-butyliodine doping during the film growth, whereas p-type doping was carried by treating the undoped layers with alkaline metal compound (Na2Te) and excimer laser radiation. Highly conductive n-and p-layers were thus obtained which formed good ohmic contact with aluminum and gold electrodes, respectively. Using this technique, n-and p- layers were formed on intrinsic CdTe substrate to form p-i-n diode. This p-i-n structure showed a good diode characteristics and good sensitivity to X-ray radiation with dark current in the order of nA/mm 2 at room temperature.