What principle does a semiconductor laser operate on?
A Stimulated emission
B Electromagnetic waves
C Photovoltaic effect
D Thermionic emission
A semiconductor laser operates based on the principle of stimulated emission. When an electron in the conduction band recombines with a hole in the valence band, it releases energy in the form of coherent light, producing laser action.
What is the main difference between LED and laser diode operation?
A Output power
B Light coherence
C Emission wavelength
D Material used
The key difference between LEDs and laser diodes is light coherence. Laser diodes emit coherent light (in phase) with a narrow wavelength range, while LEDs emit incoherent light, producing broader wavelength emissions.
What is the energy band gap of a typical semiconductor material like silicon?
A 0.5 eV
B 1.5 eV
C 2.0 eV
D 1.1 eV
Silicon has an energy band gap of approximately 1.1 eV. This band gap allows it to function efficiently in semiconductor devices, such as diodes, transistors, and solar cells, at room temperature.
What happens when the forward voltage of a diode is increased beyond the threshold?
A The current increases sharply
B No change in current
C The diode stops conducting
D The diode behaves like a resistor
When the forward voltage across a diode exceeds the threshold voltage (typically around 0.7V for silicon diodes), the diode conducts current, and the current increases rapidly as the voltage is increased further.
What does the current voltage (I V) characteristic of a semiconductor diode show?
A Linear relationship
B Parabolic relationship
C Exponential relationship
D No relationship
The I V characteristic of a semiconductor diode exhibits an exponential relationship, meaning that as the forward voltage increases, the current increases exponentially. In reverse bias, the current is very small until breakdown occurs.
What is the role of doping in semiconductor materials?
A Change conductivity
B Increase resistance
C Decrease current
D Change band gap
Doping introduces impurities into semiconductor materials to alter their electrical properties. By adding donor (n type) or acceptor (p type) impurities, doping changes the conductivity of the material, making it useful for devices like diodes and transistors.
What is the significance of minority carriers in a semiconductor device?
A Control current
B Increase conductivity
C Contribute to reverse current
D Decrease efficiency
Minority carriers are the less abundant charge carriers (electrons in p type and holes in n type). They contribute to the reverse current in a diode and play a role in the breakdown region of the I V characteristic.
In a diode, what does reverse breakdown occur?
A Forward voltage exceeds threshold
B Current becomes zero
C The diode becomes non linear
D Reverse voltage exceeds a certain value
Reverse breakdown occurs when the reverse voltage applied to a diode exceeds a certain value (typically called the Zener breakdown or avalanche breakdown voltage). At this point, the diode starts to conduct heavily in reverse, potentially damaging the diode.
What type of semiconductor is created by adding donor atoms?
A P type
B N type
C Intrinsic
D Conductive
N type semiconductors are created by doping with donor atoms, which have extra electrons compared to the host semiconductor material. These extra electrons increase the electrical conductivity of the semiconductor by providing additional charge carriers.
How does temperature affect the conductivity of a semiconductor?
A Increases conductivity
B Decreases conductivity
C No effect
D Increases resistance
As temperature increases, more electrons gain enough energy to jump from the valence band to the conduction band, increasing the number of free charge carriers. This leads to an increase in the semiconductor’s conductivity.
What is the primary function of a photodiode?
A Emit light
B Amplify signals
C Regulate voltage
D Detect light
A photodiode is designed to detect light and convert it into electrical current. It operates by absorbing photons, which excite electrons and generate current. Photodiodes are essential in optical communication and light sensing applications.
In a diode, what happens when it is forward biased?
A It blocks current
B It generates voltage
C It allows current to flow
D It absorbs energy
When a diode is forward biased (positive terminal to the p type and negative to the n type), the depletion region narrows, allowing current to flow through the diode. This is the typical operating condition for diodes in most electronic circuits.
What is the primary application of semiconductor lasers?
A Power supplies
B Optical communication
C Voltage regulation
D Signal amplification
Semiconductor lasers are widely used in optical communication systems, including fiber optics, where they convert electrical signals into optical signals for transmission. They provide high speed data transmission with low loss.
What is the primary feature of the band gap in a semiconductor?
A Controls light emission
B Determines temperature stability
C Controls electrical conductivity
D Controls carrier mobility
The band gap in a semiconductor defines the energy difference between the valence band and the conduction band. A smaller band gap allows easier electron movement, enhancing conductivity, while a larger gap restricts current flow.
What happens when a semiconductor material is exposed to light?
A It generates charge carriers
B It increases resistance
C It reduces carrier concentration
D It absorbs energy without effects
When a semiconductor material is exposed to light, photons excite electrons from the valence band to the conduction band, generating electron hole pairs. This phenomenon is essential in photodiodes, solar cells, and other optoelectronic devices.