avalanche region introduces a 90° phase shift between the AC signal and the electron concentration in this region. With a further increase in t, the AC voltage becomes negative, and the field in the avalanche region drops below its critical value. The electrons in the avalanche region are then injected into the drift zone which induces a current in the external circuit which has a phase opposite to that of the AC voltage. The AC field, therefore, absorbs energy from the drifting electrons as they are decelerated by the decreasing field. It is clear that an ideal phase shift between the diode current and the AC signal is achieved if the thickness of the drift zone is such that the bunch of electron is collected at the n+ – anode at the moment the AC voltage goes to zero. This condition is achieved by making the length of the drift region equal to the wavelength of the signal. This situation produces an additional phase shift of 90° between the AC voltage and the diode current. Origins In 1956 W. T. Read and Ralph L. Johnston of Bell Telephone Laboratories proposed that an avalanche diode that exhibited significant transit time delay might exhibit a negative resistance characteristic. The effect was soon demonstrated in ordinary silicon diodes and by the late 1960s oscillators at 340 GHz had been produced. Silicon IMPATT diodes can produce up to 3 kilowatts of power continuously, with higher power available in pulses. TRAPATT A microwave oscillator device with a similar structure to the IMPATT diode is the TRAPATT diode, which stands for "trapped plasma avalanche triggered transit". This mode of operation produces relatively high power and efficiency, but at lower frequency than a device operated in IMPATT mode. See also BARITT diode Gunn diode Tunnel diode References Further reading D. Christiansen, C.K. Alexander, and R.K. Jurgen (eds.) Standard Handbook of Electronic Engineering (5th edition). McGraw Hill. p. 11.107–11.110 (2005). . M. S. Gupta: Large-Signal Equivalent Circuit for IMPATT-Diode Characterization and Its Application to Amplifiers. 689–694 (Nov 1973). Microwave Theory and Techniques. IEEE Transactions Volume: 21. Issue: 11. ISSN 0018-9480 R. L. Jonston, B. C. DeLoach Jr., and B. G. Cohen: A Silicon Diode Oscillator. Bell System Technical Journal. 44, 369 (1965) H. Komizo, Y. Ito, H. Ashida, M. Shinoda: A 0.5-W CW IMPATT diode amplifier for high-capacity 11-GHz FM radio-relay equipment. 14–20 (Feb 1973). IEEE Journal Volume: