When using diodes with Al-(i-GaAs) - (n-GaAs) Schottky barrier under electron beam as amplifying structures there was obtained abnormally high coefficient of cathode amplification K_amp approximately equals 25000 under electrons energy of 10 keV and application of bias voltage in the straight direction (plus to aluminum contact radiated by electrons) of about 0,8 V. In fig. 1 there is given electro-sensitive structure (ESS) radiated by electrons with energy of 10 keV. High-ohm (10⁹ Ohm x cm) i-GaAs was forming by radiation of ions Ar with dose of 3 x 10¹³ ion/cm² and energy of 30 keV in n-GaAs (n equals 10¹⁶ cm^-3). Thickness of Al-contact was 0,1 micrometer, thickness of i-layer was 1 micrometer. ESS size was 0,42 x 0,25 mm². Under traditional reverse bias to 2V diode, structure parameters were: dark current I_T equals 1nA, capacity C equals 7 pF, K_amp equals 1600 under electrons energy of 10 keV. In fig. 2 there is shown K_amp dependence on bias voltage U_b under energy of radiating electrons 10 keV. Here and further, positive values of U_b corresponds to direct bias, negative values - to reverse bias to ESS. In fig. 2 it is seen that there is dependence maximum under U_b equals 0,8V and K_amp is 25000. Here is available abnormally high cathode amplification of presented ESS. Actually, taking into account that generation energy of electron-hole pair in i-GaAs is equal to 4,8eV we will obtain that even in ideal case (under reduction of energy losses in 'dead' layer to zero and full collection of unbalanced charge carriers) under radiating electrons energy of 10 keV, K_amp will be a value of about 2000. Additional cathode amplification (more than by an order) was obtained in our view due to operation of injecting n-i- transition. Actually, in i-GaAs Fermi level is near the middle of semiconductor forbidden zone, in n-GaAs -- near the bottom of conductivity zone, i.e. at the limits of n and i-regions there is formed a potential barrier. Under application of bias voltage to ESS practically all voltage falls to i-region due to i-GaAs high specific resistance. In i-region before n-i- transition for holes there is formed a potential pit. When radiating by electron flow in i-region there occurs generation and division of charge carriers pairs: electrons flow to electrode under positive potential (collector), holes are accumulated in potential pit near n-i-transition. Accumulation of holes positive charge leads to reduction of potential barrier and additional injection of electrons from n to i- region. Injected electrons are transferred by the field to collector and give current increase in the outer circuit that enables additional signal amplification in ESS.

Date Published: 22 June 1999
PDF: 4 pages
Proc. SPIE 3516, 23rd International Congress on High-Speed Photography and Photonics, (22 June 1999); doi: 10.1117/12.350488

Published in SPIE Proceedings Vol. 3516:
23rd International Congress on High-Speed Photography and Photonics
Valentina P. Degtyareva; Mikhail A. Monastyrski; Mikhail Ya. Schelev; Alexander V. Smirnov, Editor(s)