A model to explain the behaviour of GaN photoconductive detectors is proposed, and it is based on the idea of a volume modulation rather than a carrier density modulation. Space charge regions inside the semiconductor produce a variation of the conductive volume when carriers are photogenerated. The strong non-exponential photocurrent decays result from carrier capture processes over the barriers associated with space charge regions. By means of computer simulation, this model explains quite well the behaviour of current GaN photoconductor devices and predicts their time response, temperature dependence and responsivity properties.

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GaN photoconductive detectors have been fabricated on sapphire substrates by metal organic vapor phase epitaxy and gas-source molecular beam epitaxy on Si (111) substrates. The photodetectors showed high photoconductor gains, a very nonlinear response with illuminating power, and an intrinsic nonexponential photoconductance recovery process. A novel photoconductor gain mechanism is proposed to explain such results, based on a modulation of the conductive volume of the layer.

This paper shows that today's modelling of electrical noise as coming from noisy resistances is a non sense one contradicting their nature as systems bearing an electrical noise. We present a new model for electrical noise that including Johnson and Nyquist work also agrees with the Quantum Mechanical description of noisy systems done by Callen and Welton, where electrical energy fluctuates and is dissipated with time. By the two currents the Admittance function links in frequency domain with their common voltage, this new model shows the connection Cause-Effect that exists between Fluctuation and Dissipation of energy in time domain. In spite of its radical departure from today's belief on electrical noise in resistors, this Complex model for electrical noise is obtained from Nyquist result by basic concepts of Circuit Theory and Thermodynamics that also apply to capacitors and inductors.