What is Bandgap: Definition and 36 Discussions

In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow (see carrier generation and recombination). Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.

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  1. N

    A Experimental Semiconductor Bandgap Databases

    I'm looking for experimental bandgap information to compare it to DFT calculations from Materials Project and OQMD. Could anyone recommend some?
  2. Mayan Fung

    I Can Theoretical Models Predict Direct Bandgap Materials for Solar Cells?

    I am working on some research on solar cells which prefer a direct bandgap then an indirect one for the light-harvesting layer. In many works of literature, people present some measurements to tell whether the material has a direct/indirect bandgap. However, is there any criteria for a...
  3. T

    A Criticality, phase transitions and closing bandgap

    At critical points, when correlation lengths diverge near a phase transition, people often say that the spectral gap closes, which is to my understanding just the energy difference between the ground state and the first excited state (the first two eigenvalues of the hamiltonian). How should we...
  4. chrononaut 114

    "From your data, is the bandgap of ZnSe direct or indirect?"

    (urgent) Hi, This question was apart of an assignment sheet that I was given in 'Experimental Physics III' after having completed and obtained data for the practical called 'The Bandgap Energy of Semiconductor ZnSe'. Cheers Below is some screenshots of the (Matlab-processed) data we obtained...
  5. M

    I Voltage Relationships in Diodes: Exploring Bandgap, Temp & Flux

    Hello, does anybody know if there is a connection between the voltage (work) for the bandgap of a diode, the temperature voltage and the flux voltage?
  6. Martel_lu

    I Bandgap Energy and refractive index

    The statement that the higher the bandgap energy Eg, the lower the refractive index of material is confusing me. If I start from two equations. Eq1: Eg=hc/lamda_g Eq2: lamda=lamda_0/n Higher Eg means lower lamda_g. It means in order to have the light in semiconductor material with wavelength...
  7. S

    Why Do Different Semiconductors Exhibit Varied Transmittance Levels?

    Homework Statement I recently completed an experiment where I measured the transmittance of a set of samples (different semiconductors). I'm trying to understand why the transmittance was different for different samples. Only just started learning some solid-state physics. The spectrum (I...
  8. C

    Bandgap Engineering simulation

    Hi, im looking to simulate Bandgap diagram of an heterojunction of AlGaAs/ GaAs with metal schottky contacts. can anyone please recommend me of a program that can perform this task? i'll be glad to know. thanks
  9. K

    Semiconductor intrinsic Fermi Level? Bandgap Energy?

    http://ecee.colorado.edu/~bart/book/book/chapter2/ch2_6.htm#2_6_2 equation (2.6.24) we have this equation for fermi level, but I wonder how this works though? In the lecture, we assumed Ec=Eg and Ev=0 to get E_gap/2. but I wonder how (Ec+Ev)/2 actually gives E_gap/2 instead of Ec-Ev=Eg
  10. S

    Does n type doping decrease or increase the bandgap?

    Hi, I understand that a n type doping will increase the number of electrons, and those electrons will go to the conduction band since the valence band is already filled. I don't exactly understand the effect on the bandgap. Thanks!
  11. A

    What Causes the Forbidden Gap in Semiconductors?

    Can anybody explain my what is the origin of this forbidden gap? I mean how it was created and what is the physics behind this issue?
  12. J

    Possibility of optical absorption by defect level in bandgap

    Hi, I have a tricky question regards the absorption of photons by semiconductor. Say I got a piece of semiconductor with Eg=4eV. Inside the bandgap, there are two defect levels, and each of them have a trapped electron. One of the defect has the energy level that is 1eV below conduction...
  13. C

    Wide bandgap semiconductor -- why higher temperature tolerance?

    I was wondering if anyone knows the relationship with temperature and frequency tuning in wide bandgap semiconductors. I just want to know why wider bandgaps have higher temperature tolerance and why does that mean high frequencies can be achieved? Explanation with formulas would be great!
  14. D

    Why is black phosphorus semiconductor with direct bandgap?

    Why is black phosphorus a semiconductor with a direct bandgap? The problem is mentioned by the two following references: "The three bonds take up all three valence electrons of phosphorus,so, unlike graphene, monolayer black phosphorus is a semiconductor with a predicted direct bandgap of 2 eV...
  15. Christian0412

    Calculating Bandgaps Experimentally

    I've been doing a bit of reading on bandgaps of semiconductors and alloys of semiconductors. I was curious to know is the bandgap of a material, say Silicon, determined or calculated experimentally? How do scientists usually determine this in the lab?
  16. A

    Why doesn't Graphene have a band gap?

    Is there any simple justification about graphene having no band gap? How bout its linear E-K? Why bilayer graphene has a quadratic E-K and electric field can open a band gap there? I do not completely understand the broken symmetry argument? Also Why MoS2 which has similar structure, do not...
  17. A

    Can I get Bandgap of 3D material with 1D Hamiltonian

    Hi All, Greetings! I have a 3d material and I use result from first principal for getting the potential (U(x,y,z)). I then find average U(x) from U(x,y,z). Now if I write one dimensional Hamiltonian in X direction and use this value of U(x), can I get bandgap of the original 3d material (I...
  18. A

    What Bandgap Energy Range is Required for Blue LEDs?

    Homework Statement Blue light corresponds to free space wavelengths of approximately 450 to 495 nm. If we want to use a semiconductor to make a blue LED, what range of energies must the semiconductor's bandgap fall within? Express your answer in units of electron volts(eV). What is an...
  19. F

    Solar cell open circuit voltage and bandgap

    Hello Forum, if we take a silicon solar cell, the open circuit voltage is about 0.5V. the current increases as the solar cell area and illumination increases. But the 0.5 V output voltage does not change as the area and illumination level vary...Why? It must have something to do with...
  20. Darth Frodo

    Calculating Bandgap Energy in Silicon Using Conductivity Measurements

    Homework Statement The conductivity of an intrinsic silicon sample is found to be 1.02 mS.m-1 at 297.2 K and 2.15 mS.m-1 at 307.9 K. What is the bandgap energy in silicon? Homework Equations ni = Ns(e^{\frac{-E}{2kT}}) \sigma = eni(μp + μn) The Attempt at a Solution I'm having...
  21. C

    Si Bandgap in Device Modeling (Silvaco Atlas)

    I recently noticed that in Silvaco Atlas (device modeling software), the default bandgap of silicon is given as 1.08 eV. This is at 300 K, no bandgap narrowing, and no other secondary effects - it is default. However, most (all?) of the modern references (e.g. Sze, Streetman, Pierret) give the...
  22. B

    What has bandgap gotta do with binding energy and stability?

    Hi, Could someone clarify the following statement please? "ZnO has a bandgap of 3.4 eV at room temperature and a free exciton binding energy of 60meV which is much larger than the room temperature thermal excitation energy (25meV) making them stable at rtp." Does it mean that at rtp, we...
  23. N

    Calculating Material Bandgap Using Quantum Theory

    Quantum theory says that the energy, E , (in eV) of a photon of wavelength λ is E = hc/eλ, where h is Planck's Constant, c is the velocity of light and e is the charge on an electron. Calculate the bandgap of a material which absorbs electrons shorter than 500nm.
  24. U

    At 0k, why is fermi level halfway in bandgap?

    At 0k, why is fermi level halfway in bandgap?? Fermi Level is defined as the maximum energy an electron posesses at 0k, which appears to be midway in the bandgap. I learned that in the bandgap, there are no available states (i.e. no wavefunctions of electrons) hence, no electrons can possibly...
  25. J

    Error in bandgap measurements of n-type Ge

    In conducting an experiment to measure the bandgap of n-type Ge using the 4-probe method, heating the sample and measuring the change in voltage across the probes as it cooled, it was necessary to change regularly between the milliammeter and the millivoltmeter setting on the instrument to...
  26. C

    Small bandgap IR detectors need to work in crogenic temperature

    Is anybody can give me a detailed explanation or reference why the small bandgap IR detectors (eg. InSb photodetecotr) need to work in the cryogenic temperature? In addition, anybody knows what is carrier capture time? Since some article said the photodetector detectivity is proportional to...
  27. T

    Bandgap in a weak periodic potential

    Using the Schrodinger equation for an electron in a periodic potential where U(r +R) [R is the translation vector R=n1a1+n2a2+n3a3 and ni are intergers and ai are teh primitive lattice vectors, G is for reciprocal lattice G=n1b1+n2b2+n3b3 and ni are intergers and bi= (2PI*aj x ak)/(a1 . a2 x...
  28. S

    Effective mass versus bandgap

    Hello- I feel that this is a "graduate-level" question, so I hope that this question is not found to be insultingly easy. Can someone help me gain an understanding of why bandgap and electron effective mass in semiconductors are proportional to one another (e.g. trend of C, Si, Ge...
  29. T

    When the electrons hit the bandgap

    how to calculate the phase change of the reflection when the electrons hit the bandgap of a metal from another metal through a common interface? For sure i know there must be a large quantity of them reflected back. but how to model this using the nearly free electron?
  30. D

    Bandgap Values for GaAs and Si

    I'm doing a lab report on optical absorption of semiconductors. As such I would like to verify the values of the bandgap Eg which I have calculated through experiment. I tried searching Google but I got a lot of results to technical papers which didn't help at all. I would like to know if...
  31. K

    Is there relationship between resistivity and bandgap?

    is the material, which has a larger bandgap, more resistive:confused: ? thanks for answering:smile: kit
  32. I

    Calculate Bandgap Voltage for GaAs Photodiode: 5V Reverse Bias

    Hello, I am having a bit of trouble with the following problem: Assuming a built in voltage equal to the bandgap voltage, calculate the slowest possible transmit time for a carrier with 5V reverse bias applied to the GaAs photodiode. I would be able to do this problem without difficulty if...
  33. Q

    Indirect vs. Direct Bandgap Semiconductors

    I have one question to trouble you. Why some semiconductors have a direct bandgap, while some have an indirect bandgap? Is there any very crude "thumb rule" of predicting/justifying it? Thanks a lot
  34. S

    Why amorphous phase materials have wider bandgap?

    I'm wondering why the amorphous phase materials have wider bandgap compared to its crystalline phase. To my best knowledge, the bonding mechanism does not changed as the material transform from crystalline phase to amorphous phase. So what causes it has larger bandgap? ST
  35. H

    Indirect bandgap in carbon nanotube

    hello everybody, i want to ask about the indirect bandgap in carbon nanotube, how its look like? is there any article, literature or links about that? and i will be very glad if anybody can answer this. thankyou
  36. E

    Question About Indirect vs. Direct Bandgap Semiconductors

    Let's say I have an unknown material and I wanted to determine whether it is has an indirect or a direct bandgap. Is there a standard experiment for doing this without assuming we know the bandgap energy a priori? eNtRopY