Flashcards

Week 5 LNs

R S C Solid State Year 4 Inglês 21 flashcards

Flashcards do conjunto (21)

1Explain briefly the differences between reverse and forward bias for a pn junction
2Explain the depletion zone in a pn junction and the effect of an externally applied voltagean insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or forced away by an electric field
So at the p/n interface there is low free charge carrier density, with a higher resistivity than outside the space. charge region.
If U is approx VD the potential step is removed. Negative U increases the potential step.
3State the relations for depletion zone thickness for unbiased and biased
4Define generation and recombination currents Describe U when it is; 0 less than 0 greater than zeroIn solid-state physics of semiconductors, carrier generation and carrier recombination are processes by which mobile charge carriers (electrons and electron holes) are created and eliminated.
5Prove generation currents are bias independent
6Describe solar cells in the context of pn junctionsA solar cell is essential a PN junction with a large surface area. The N-type material is kept thin to allow light to pass through to the PN junction. Light travels in packets of energy called photons. The generation of electric current happens inside the depletion zone of the PN junction.
7For solar cells; use a sketch to derive and define the fill factorFill factor (solar cell), the ratio of maximum obtainable power to the product of the open-circuit voltage and short-circuit current.
8Define LEDs in the context of pn junctionsA light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons.
Light-emitting diodes are heavily doped p-n junctions. Based on the semiconductor material used and the amount of doping, an LED will emit coloured light at a particular spectral wavelength when forward biased.
9Define the Bipolar Transistor What happens at; emitter base p base region If is a base collector pn junction If there is voltage amplificationa solid-state device in which the current flow between two terminals (the collector and the emitter) is controlled by the amount of current that flows through a third terminal (the base).
10Define the FET Where are the used How are they madeThe field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.
11For the FET, explain when it is off and on
12Define and state the reflectance equation from Fresnel with the aid of a drawingThe s polarization refers to polarization of a wave's electric field normal to the plane of incidence (the z direction in the derivation below); then the magnetic field is in the plane of incidence. The p polarization refers to polarization of the electric field in the plane of incidence (the xy plane in the derivation below)
The angles that the incident, reflected and refracted rays make to the normal of the interface are given as θi, θr and θt, respectively. The relationship between these angles is given by the law of reflection.
For the case of normal incidence, θi = θt = 0, and there is no distinction between s and p polarization. Thus, the reflectance simplifies to the shown relation
13State the classical EM relations for P and D in terms of E, stating what each of them are Define the dielectric function Define the complex index of refraction in terms of the dielectric functionThe dielectric function is the response of a system to an external electric field
In the relation for the CIR n1 is the real part and n2 the imaginary part
14Derive the dielectric function of the free electron gas and the plasma frequencyIn the long wavelength limit the wave vector dependence is dropped. Looking at this as a free electron in an electric field and using its equation of motion, by assuming E and x oscillate as the exponential, relations can be found in terms of frequency. The dipole moment can be expressed in terms of the angular frequency (equal to the displacement of the charge times the charge itself). The polarisation is a dipole moment density and can be expressed in terms of frequency. Using the general relation for the dielectric function and the relations for P and E, the dielectric function of a free electron gas can be found. As the frequencies must always be positive the DF must always be less than one. From this the plasma frequency of the free electron gas can be found.
15For dispersion relations for EM waves, describe the type of waves and solutions for when dielectric function is; greater than zero, less than zero, equal to zero, complex, equal to infinity
16For transverse optical modes in a plasma; What is the plasma made up of? What is its plasma frequency?
17For transverse optical modes in a plasma; State the wave solutions for E and D When omega is greater and less than modified plasma freq
18Explain why many metals have plasma frequencies in the UV region (HMR)
19For the complex optical constants; state the exponential relation which includes oscillation and damping contributions
20Describe the plasmonsA plasmon is defined as a quantum of collective electron oscillation in a solid. It is also referred as a bulk plasmon. It may reveal itself in metals, doped semiconductors and other materials, where the concentration of charge carriers is sufficient. Theyre a collective longitudinal excitations
of the electron gas.
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