p-n photodiode is fabricated from a semiconductor with a band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?



Correct option is

0.21 eV

The energy of  wavelength photon is 





           = 0.21 eV. 

As photon energy is less than the energy of band gap (= 2.8 eV), these photons will not be absorbed by the semiconductor (light will be transmitted through the semiconductor). As such, the photodiode cannot detect the given wavelength.



In a pnp transistor, the p-type crystal acts as


The current gain in a common emitter transistor is


If the input and output resistances in a common-base amplifier circuit are  respectively, what is the voltage amplification when the emitter current is 2 mA and current gain ?


When npn transistor is used as an amplifier


When a pn junction is reverse biased, the flow of current across the junction is mainly due to


The V-i characteristic of a silicon diode is given in the figure. Calculate the diode resistance in forward bias at V = +2 volt.  


A forward-biased p-n junction diode has a potential drop of 0.5 V which is assumed to be independent of current. The current in excess of 10 mA through the diode produces so much heating that burns the diode. If we have a 1.5 V battery to bias the diode, resistor must be used in series with the diode so that the maximum current does not exceed 5 mA?   


A Si diode (p-junction) is connected to a resistor R and a biasing battery of variable voltage VB. Assume that diode requires a maximum current of 1 mA to be above the knee point (0.7 V) of its V-i characteristic curve. Also assume that the voltage V across the diode is independent of current above the knee point. If VB = 5 V, what should be the maximum value of R so that the voltage V is above the knee-point voltage?   



In the circuit (a), calculate the current in the  resistance. Assume that each diode is of silicon (Si) and its potential barrier is 0.7 volt, and forward-resistance is .


The depletion layer in the p-n junction is formed by