Tham khảo tài liệu 'silicon carbide materials processing and applications in electronic devices part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 340 Silicon Carbide - Materials Processing and Applications in Electronic Devices To understand the operation and performance of IMPATT devices and oscillators knowledge of the basic IMP ATT phenomena is required and briefly discussed in the following section. To build an IMPATT oscillator the device has to be mounted in a suitable microwave mm-wave circuits. The performance of the oscillator strongly depends not only on the device but also on the circuit in which the device is embedded .The various microwave mm-wave circuits that are being widely used to construct IMPATT oscillators have been reviewed briefly. A brief review of the fundamental physical processes involved in IMPATT action followed by a review of the various IMPATT structures and oscillators will be presented in this section. The factors which determine the avalanche delay and the transit time delay for high frequency operation of IMPATT will also be briefly discussed. High field properties of charge carriers in IMPATT devices The different scattering interactions between the charge carriers and the lattice lead to the emission of both acoustic and optical phonons which give rise to the saturation of carrier s drift velocity in semiconductors which is one of the fundamental physical phenomenon involved in IMPATT action. Drift velocity of charge carriers has been observed to be linear upto the electric field 104 and it reaches a scattering limited value independent of the electric field when the field is very high 106 . At low values of electric field E which the principal scattering phenomenon is acoustic phonon the drift velocity vd of charge carriers in semiconductor varies as vd oE 1 Where ỊẤ0 is the low field mobility and can be expressed as _ .-2- . V T0 ri . __2 _ m v 2 Where q is the charge of the electron m is the effective mass of the carrier To is the relaxation time and v is the carrier velocity. The brackets in the above expression indicate Maxwellian average. In the low
