Avalanche gain

Hurwitz and Hsieh [8.81] have reported avalanche gains for 1.2 pm radiation in excess of 12 with 150 ps rise times and 45 % quantum efficiencies in epitaxial layers of Gain AsP on InP substrates. The APD sensitive area is an etched mesa of 150 pm in diameter. The authors feel that this alloy combination can provide avalanche sensitivity with good lattice matching over the spectral range of 0.9 to... 

Avalanche Photodiode (APD)—A photodiode designed to take advantage of avalanche multiplication of photocurrent. As the reverse-bias voltage approaches the breakdown voltage, hole-electron pairs created by absorbed photons acquire sufficient energy to create additional hole electron pairs when they collide with ions thus a multiplication or signal gain is achieved. 

From the function of a channeltron/channelplate detector it is obvious that high gains are desirable. However, ion feedback and space charge effects limit the gain with increasing charge of the electron avalanche, electron impact ionization with molecules of the residual gas or molecules desorbed under electron bombardment from the channel surface occurs more frequently. The ions produced are then accelerated towards the channel input. If such an ion hits the surface at the channel entrance, it may release an electron which again can start an avalanche of practically the same size, i.e., it causes after-pulses. 

Atmospheric pressure plasmas, just like most other plasmas, are generated by a high electric field in a gas volume. The few free electrons which are always present in the gas, due to, for example, cosmic radiation or radioactive decay of certain isotopes, will, after a critical electric field strength has been exceeded, develop an avalanche with ionization and excitation of species. Energy gained by the hot electrons is efficiently transferred and used in the excitation and dissociation of gas molecules. In a nonequilibrium atmospheric pressure plasma, collisions and radiative processes are dominated by energy transfer by stepwise processes and three-body collisions. The dominance of these processes has allowed many... 

Intrinsic breakdown is explained as follows. When the field is applied the small number of electrons in thermal equilibrium in the conduction band gain kinetic energy. This energy may be sufficient to ionize constituent ions, thus increasing the number of electrons participating in the process. The result may be an electron avalanche and complete failure. Intrinsic breakdown strengths are typically of the order of 100 M V m 1. 

Crystalline silicon devices take advantage of avalanche multiplication to enhance the gain without the problems of the secondary photoconductor. Carriers are accelerated under the field until their energy is high enough to cause impact ionization. The requirement is roughly that... 

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