In graphs of the electronic band structure of solids, the band gap is the energy difference in electron volts between the top of the valence band and the bottom of the. Thickness effect on the band gap and optical properties of germanium thin. This paper states the step by step experimental approach in determining the band gap of a semiconductor germanium. The term is used in solidstate physics and chemistry band gaps can be found in insulators and semiconductors. This band is considered to be due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties and which are considered to be associated with vacancies. Band structure and carrier concentration of germanium ge. To determine band gap of given semiconductor material. Why does germanium have a smaller energy bandgap than. Values of e go and for various materials are given in table i. The energy gap is determined from the measured values.
It is a iiiv direct band gap semiconductor with a zinc blende crystal structure gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared lightemitting diodes, laser diodes, solar cells and optical windows. Germanium is an ideal candidate to achieve a monolithically integrated laser source on silicon. The energy band gap, e g, is located between the two bands. Roomtemperature direct band gap electroluminescence from germanium 111. Now zoom on the area for which you want to calculate the band gap and note down the. Germanium ge is a groupiv indirect band gap semiconductor but the difference between its direct and indirect band gap is only 140 mev. Open the absorption graph of the material, which is obtained from the uv vis spectroscopy. The principle of pauli exclusion teach us that no two electrons in a solid may have the same condition. Gallium arsenide gaas is a compound of the elements gallium and arsenic. Look at the periodic table, youll see that germanium is under silicon, and hence has an extra shell higher principal quantum number due to it having a higher atomic number more electrons. What is the photon wavelength in nanometers of the emission generated by this photoexcitation.
It is also possible to construct layered materials with alternating compositions by techniques like molecular beam epitaxy. They both have approximately the same latticeconstant, but strongly differing bandgaps 0. Raw html w a v e l e n g t h i n t e n s i t y 200 220 240 260 280 300 0. We calculate the electronic structures of germanium nanowires by taking the effectivemass theory.
Making germanium, an indirect band gap semiconductor. Nature of the band gap of silicon and germanium nanowires. In this paper, w e establish the direct band gap optial gain theory of germanium nanowires. Germanium is an elemental semiconductor with a band gap, e g, of 0. Determining the band gap of germanium determining the band. In this experiment, the band gap energy of undoped germanium was measured and found to be 0. The band gap of a semiconductor is the minimum energy required to excite an electron that is stuck in its bound state into a free state where it can participate in conduction.
Germanium is considered a technologycritical element. Within the precision of our experiment, the results obtained are in good agreement with the known value energy gap in silicon. Several methods for the experimental determination of the band gap in silicon and germanium have been discussed. The lowestenergy gap that is free from atoms is known as the conduction band. Effects of p, as, and sb heavy doping on band gap narrowing. Emission of directgap band in germanium with gegesn layers. To determination of the band gap of the semiconductor using the four probe method. W e take the e ectivemass theory to investigate the electronic structures an d optical gain of ge.
The optical constants of amorphous ge are determined for the photon energies from 0. Pdf a method for determining the band gap in germanium and silicon at 0 k based upon the temperature dependence of the electrical. This element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry. The measurement data permits determination of the band gap between the valence band and the conduction band in germanium. Hall effect measurements for determining the band gap.
In photoluminescence studies, the occurrence of a new emission line was identified as ge related and explained as a donoracceptorpair. The energy band diagram of germanium is shown below. We present here a complementary study on germanium doping of the wider band gap cugase2 cgs chalcopyrite. Furthermore, ge is an indirect and gaas is a direct semiconductor.
Experimental estimation of the band gap in silicon and. Gap between the valence band and conduction band in this material is very small. Graph between 103t as abscissa and log 10 i s as ordinate will be a straight line having slope 5. When the band gap energy is met, the electron is excited into a free state, and can therefore participate in conduction. In a crystalline solid as a result of interaction between tremendous numbers of atoms in the crystal the energy levels are split up and form bands of allowed energy which contains almost continuum of levels. The ek relation of the ge conduction band is described also by eq. What is the minimum energy of incident light that will result in the photoemission. Germanium compounds are also used for polymerization catalysts and have most recently found use in the production of nanowires. Semiconductor, band theory, forbidden band, intrinsic conduction, extrinsic conduction, impurity depletion, valence band, conduction band. Band gap simple english wikipedia, the free encyclopedia. E g e g0 t 4 where e g0 is the band gap at zero temperature, and is a constant for a given semiconductor. If the optical absorbance of narrow band gap semiconductors can gradually be tuned to absorb in the visible region by controlling the particle size, the overall photoactivity of the hybrid semiconductor system can be greatly expanded. Here, we demonstrate that a thick germanium layer can be transformed from an indirect into a direct band gap semiconductor by using silicon nitride stressor layers. Direct band gap germanium microdisks obtained with silicon.
With this experiment we will be able to determine the band gap of a semi conductor material. Physical structure of matter band gap of germanium 5. To gain a fundamental understanding of the operation of a solar cell, it is essential to know what the concept of gap theory exactly entails. Similarly one finds the energy bandgap for germanium and gallium arsenide, as well as at different temperatures, yielding. Principle the conductivity of a germanium testpiece is measured as a function of temperature. These discrete shells in a solid become almost continuous bands, the socalled energy bands. A method for determining the band gap in germanium and silicon at 0 k based upon the temperature dependence of the electrical conductivity of a pn junction is described. Band gap, in solidstate physics, a range of energy levels within a given crystal that are impossible for an electron to possess.
Uv vis spectroscopy band gap calculator calculation tutorial. In the intrinsic temperature range, direct effects due to thermal band to band excita tions are negligible. Regression of the conductivity versus the reciprocal of the absolute temperature. Band gap in a semiconductor diode the band gap is one of the most important characteristics in a semiconductor. Determining the voltage drop at an undoped ge crystal as a function of the temperature when the. In this paper, we establish the direct band gap optial gain theory of germanium nanowires. The band structure of a semiconductor gives the energy of the electrons on the yaxis and is called a band diagram. Hall effect measurements for determining the band gap energy. Hall effect measurements for determining the band gap energy of undoped germanium, including the conductivity, charge carrier type, concentration and mobility for ntype and ptype doped germanium hassan mirza1 and danny morris1 1school of physics and astronomy, queen mary, university of london, london e1 4ns, england received 28 march 20. Silicons valence orbital is 3p2, while germanium is 4. Band gap energy, which is dependent on the material, is also temperature dependent and decreases with temperature to. Silicon and germanium have similar electron affinities 4. The theoretical directbandgap optical gain of germanium nanowires article pdf available in scientific reports 101.
Subband gap photodetection from the titanium nitride. Band gap engineering is the process of controlling or altering the band gap of a material by controlling the composition of certain semiconductor alloys, such as gaalas, ingaas, and inalas. It is the width of this energy gap that makes a semiconductor a semiconductor. Setup and procedure the experimental setup is shown in fig. In this experiment you will use the temperaturevoltage curve of a diode under constant current to determine the band gap for the diode material. Narrow band gap semiconductor an overview sciencedirect. Calculate the wavelength photoemission generated by this interaction. As the band gap energy of semiconductors plays a fundamental role in electrical and optical properties, it is important and necessary to investigate the band gap. The hall coefficients of ntype and ptype doped germanium samples were measured and found to be respe. Germanium chip using four probe setup musa abubakar bilya1, mujahid hassan sani2 1physics department, jodhpur national university, 342001, boranada, rajasthan state of india abstract. In figure four probes are spaced s1, s2, s3 and s4 apart.
The highly energetic group in which electrons are located is called the valence band. Temperature dependence of semiconductor conductivity originally contributed by professor e. A band gap, also called a bandgap or energy gap, is an energy range in a solid where no electron states can exist. Unfortunately bulk germanium is an indirect band gap semiconductor. The test piece on the board has to be put into the halleffectmodule via the. A semiconductor either doped or intrinsic always possesses an energy gap between its valence and conduction bands fig. Semiconductor, band theory, forbidden band, intrinsic conduction. The kronigpenney model demonstrates that a simple onedimensional periodic potential yields energy bands as well as energy band gaps. Determining the band gap of germanium determining the.
Here, we have demonstrated a hotcarriermediated sub band gap photodetection in germanium based planar heterojunction devices. Germanium is a material with special properties such as high mobility of electrons and holes. The theoretical directbandgap optical gain of germanium. In practice, most research is focused on only one particular band gap that which encloses the fermi level the energy level at which electrons exist or are below when a solid is at absolute zero temperature. Theoretical study of energy gap for silicon and germanium under. Photoexcited hot carriers through nonradiative decay offer new opportunities for harnessing longer wavelength light.
We take the effectivemass theory to investigate the electronic structures and optical gain of ge nanowires with the diameters from 6 nm to 18 nm, and the indirect 111 l valley is taken into account. Narrow band gap semiconductors with appropriate band structure can play a similar photosensitizing role as organic dyes when they are coupled with tio 2 8486. Temperature dependence of semiconductor conductivity. This particular band gap is present in semiconductors and insulators and thus is the only band gap relevant to the discussion of electronics and. Principle and task the conductivity of a germanium testpiece is measured as a function of temperature.
The planar samples that form in situ germanium titanium nitride getin interfaces are fabricated by the dc sputtering technique, and the generation. There are, to my knowledge, no simple rules on how to construct the band diagram from just a few material parameters. Material semiconductor crystal lattice energy band system name symbol structure perioda gap ev type iiiv aluminum phosphide alp z 5. It is also possible to construct layered materials with alternating compositions by techniques like molecularbeam epitaxy. Why silicon band gap energy is more than germanium. The conductivity of a germanium testpiece is measured as a function of temperature. So bandwidts are increased, leaving less room for gaps. Generally, a material will have several band gaps throughout its band structure the continuum of allowed and forbidden electron energy levels, with large band gaps. Effective density of states in the conduction band. Hence, a very small energy is sufficient to lift the electrons from the valence band to the conduction band. The effective masses of the holes in the three bands. An increase in temperature changes the chemical bonding as electrons are promoted from valence band to conduction band.
The band gap energy e g in silicon was found by exploiting the linear relationship between the temperature and voltage for the constant current in the temperature range of 275 k to 333 k. Principle the conductivity of a germanium test sample is measured as a function of temperature. In intrinsic semiconductors there is an equal number of electrons and holes in the material. The band gap itself varies linearly with tover a large temperature range. Elemental semiconductor an overview sciencedirect topics. The band gap eg of the semiconductor germanium ge is 0. It is this materialspecific property that explains the behaviour of the semiconductor in a solar cell to a large extent. It has been shown that when ge is subjected to a tensile strain and a heavy n doping level, roomtemperature photoluminescence pl can be greatly enhanced. If a voltage is applied, there is no conduction of electrons because there. Roomtemperature direct bandgap electroluminescence from. This is in agreement with and very close to the literary value of 0.
Determination of the bandgap of the semiconductor using. Energy band gap kit containing a pn junction diode placed inside the temperature. Liu2 1school of electrical and electronic engineering, nanyang technological university, singapore 639798. While it is an oversimplification of the threedimensional potential and bandstructure in an actual semiconductor crystal, it is an instructive tool to demonstrate how the band structure can be calculated for a periodic potential, and how allowed and forbidden. But ge is an indirect bandgap material, so an electron transits from the conduction band to the valence band mainly by phononassisted recombination with nonradiation process, which results in slow and inefficient direct optical recombination. Optical properties and electronic structure of amorphous. The pn junction is an important element of most electronic devices, from a simple diode to a. Thickness effect on the band gap and optical properties of. For the 111 lvalley, we expand the envelope wave function using bessel functions to calculate the energies of the electron states for the first time.