Evaluation of doping levels in active layers of MESFETs

Summary form only given. We have presented a detailed survey of the different processes of active layer doping determination and compared their advantages and disadvantages. The evaluation of the doping levels in the active layer of the MESFET wafers is important since they determine the charge in the channel of the transistors. The charge in the channel of the transistors, on the other hand, controls the gate-recess etching of the transistors. Thus for proper fabrication of the transistor devices, the knowledge of the active layer doping is important. The conventional methods of doping determination are the Hall technique and the electrochemical voltage profiler technique. These methods are quite accurate and are widely used in spite of their destructive nature and the difficulty involved in the measurements. The former measures the net carrier concentration (Nd-Na) and the latter measures only the donor concentration Nd. The photoluminescence parameter, FWHM, can be used as an alternative to the above techniques for measurement of the doping levels nondestructively. But this requires careful measurements at 77 K, and full spatial mapping of the wafer for increasing accuracy. We will discuss the experimental results in detail and compare with theoretical calculations.