Gap Definition and 288 Threads

Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with an indirect band gap of 2.24 eV at room temperature. Impure polycrystalline material has the appearance of pale orange or grayish pieces. Undoped single crystals are orange, but strongly doped wafers appear darker due to free-carrier absorption. It is odorless and insoluble in water.
GaP has a microhardness of 9450 N/mm2, a Debye temperature of 446 K (173 °C), and a thermal expansion coefficient of 5.3 ×10−6 K−1 at room temperature. Sulfur, silicon or tellurium are used as dopants to produce n-type semiconductors. Zinc is used as a dopant for the p-type semiconductor.
Gallium phosphide has applications in optical systems. Its static dielectric constant is 11.1 at room temperature. Its refractive index varies between ~3.2 and 5.0 across the visible range, which is higher than in most other semiconducting materials.

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  1. S

    Air gap flux density in DC machine

    Why is it that the air gap flux density is flat topped at no load. What happens to it's shape when machine is loaded?
  2. D

    Direct and Indirect Optical Band Gap

    I've been looking on journals and textbook, as well as internet. Does anybody know if there is an equation to find out the value of direct optical band gap and indirect optical band gap? What is the difference of optical band gap, direct optical bandgap and indirect optical bandgap? also...
  3. P

    Newton's Rings and Gap Size - See Attachment

    Homework Statement A shallowly curved piece of glass is placed on a flat one. When viewed from above, concentric circles appear that are called Newton’s rings. In order to see bright rings, the gap can be: 1. 0 2. 1/4λ 3. 1/2λ 4. λ Homework Equations 1/2 λ occurs when n2>n1...
  4. O

    Gap between two displaced spheres

    This was out of a physics book, but since it's just geometry, I thought this would be the best forum to ask about it. I was reading through a derivation of the far electric field of a uniformly polarized sphere, and the author used a trick where he modeled the sphere as two displaced spheres...
  5. W

    Band gap calculation,how to choose the Kpoints?

    hello, is there anyone who can help me in the band gap calculation. my situation is that: I can calculate the band gap of sigle crystalline graphene, because i know the high symmetrical pionts of the first Brillouin zone of an hexagonal crystalline(M-G-K-M). But the problem is that...
  6. B

    Programs Will taking a gap year during my degree hurt much?

    Hi, I'm going into my junior year and I was thinking of taking a gap year to do something entirely different than Physics. Do grad schools look down on people who took a gap year during the progress of their degree? Will they require you to explain what happened during that year? Thanks! :smile:
  7. M

    Exploring Gap Exponents and Their Significance

    Gap exponents are denoted like critical exponents for higher derivatives of Gibbs potential. \Delta_l' (\frac{\partial G}{\partial H})_T=G^{(1)}\propto (1-\frac{T}{T_c})^{-\Delta_1'}G^{0} (\frac{\partial^l G}{\partial H^l})_T=G^{(1)}\propto (1-\frac{T}{T_c})^{-\Delta_l'}G^{l-1} \alpha'...
  8. E

    Consequences of Yang-Mills and Mass Gap?

    What are the consequences of a possible solution to Yang-Mills existence and mass gap problem? Are the consequences only physical or they will also have applications to other branches of science or life? If yes, what are they?
  9. M

    Interpretation of 1D Band Gap in Metallic Systems

    In a metallic system, the Fermi level is crossed either from the conducting zone into the non-conducting zone or vice versa. Is there an interpretation one can give to the direction of the crossing? In other words, if the 1D band gap diagram shows the fermi line is crossed from the...
  10. S

    Is Taking a Gap Year During Undergrad Beneficial For Graduate School Admissions?

    Hi, I've completed one year of undergrad. I started in engineering but have now decided that I want to pursue math. Before continuing, I want to take a year off to refocus and take care of other aspects of my life. I feel like I will do better if I take a year off. On the other hand, I enjoy...
  11. M

    Newbie Questions on Band Gap and Fermi Level

    I am new to solid state physics, having been in computational chemistry (quantum mechanics) for the larger part of my career. Hence have a lot of newbie like questions that are not easily answered by google/wikipedia searching. 1)In viewing a 1-dimensional band gap diagram, crossing the...
  12. J

    Difficult Schedule to Bridge Gap

    Hello everyone, I am one of those non-majors trying to get into graduate school (eventually). Long story short, I have a year left as a business major, during which time I will be taking Calculus 2 and the introductory physics w/lab sequence. I have recently met with both the graduate...
  13. P

    Spark plug/Igniter/Spark gap in PSpice

    As far as I can tell, none of these come with the student edition of PSpice. The first problem is I can't find a model for any of these things. The second problem is I don't know how to import a custom part. Worst come to worst, I could make the part myself, but once again, I have no experience...
  14. I

    Magnetic pull force with a gap

    Hello. I'm a cabinetmaker and my college physics courses are 25 years behind me now. I'd consider it a kindness if someone would answer a question for me regarding magnetism. I have a magnetic strip that is described as having 6.2 lb. of magnetic pull force per lineal foot, 1" wide and 0.020"...
  15. F

    Plan Sprinkler System Layout: Minimize # Circles for Max Coverage

    I have to plan the layout of a sprinkler system. Basically, each sprinkler shoots a radius of 7.5 feet water, and I want every part of the floor covered with water. How can I use the least number of sprinklers?
  16. C

    Solar efficiencies of photovoltaics in relation to the band gap energies?

    I'm reading a paper on photovoltaic hydrogen production and the author claims that for reasonable solar efficiencies the band gap must be less than 2.0eV. This I understand. My question is how will it effect the photon absorption if the band gap is much smaller. Say the band gap energy is...
  17. M

    Pairing gap equation weak coupling

    In the limit of weak coupling, G\overline{ρ}<<1, the BCS pairing gap equation gives that Δ \propto exp(-1/G\overline{ρ}). \overline{ρ} is the level density.This cannot be developed as a power series in the interaction strength G. Does this imply that there is a phase transition between a...
  18. E

    Energy Gap of Intrinsic Semiconductors: Temperature Dependence

    Energy gap dependence on temperature for intristic semiconductors (Si,Ge) I need help on this topic, where to find text about this, and models that describe it (Varshni's model, linear model,...)
  19. D

    How Can I Improve My Spark Gap Switch for High-Speed Photography?

    Hi everyone , this is my first post here :) . I am an auto electrician , my hobby is photography. I am interested in high speed photography and have invented a new form of photography in a way . I call it 'superspeed photography' . It involves taking a picture of something that is triggered by...
  20. A

    Is an Age Gap a Deal Breaker in Dating?

    I'm going to go ahead and put this to the board, figure I might as well. I'm 30 years old, and a pretty quiet person. Friendly, polite, but stand-offish with most people. Anyway, enough with the background. There's a girl at my work who I think is great. She's gorgeous, a little reserved, and...
  21. N

    Is It Reasonable to Assume a Prime Gap of at Least 10 Before Twin Primes?

    If we assume that the Twin Prime Conjecture is true (and thus there are infinite number of primes that are 2 apart), how reasonable is it to assume that there will be an infinite number of Twin Primes that are preceded by a prime that is at least 10 lower than the first of the Twin Primes? (I...
  22. S

    Why Can't Electrons Occupy the Band Gap in a Material?

    Hello, do you know why no electron can stay in the band gap? Is it impossible at every energy? Thank you!
  23. R

    Gap between the plates of a Thermal Electric Modules

    Dear Experts Does anyone know how big can we extend the gap between the 2 plates? Thanks. Regards Ramone
  24. E

    Exploring Element Band Gap: What Determines the Size and How Can It Be Altered?

    Might be an easy question (or not). What determines the band gap of an element? As far as I know, silicon is the most efficient single-element semiconductor because of it's small (but nonzero) bandgap. Next (as far as I know) is Selenium. I'm aware there are more efficient compounds, but...
  25. Pythagorean

    Gap junction modulators for C. elegans

    Are there any known gap junction openers/closers for C. elegans? I've googled far and wide for weeks. Trimethylamine, quinine, and carbenoxolone are known to work with connexins in mammals. They also happen to be expensive and require more paperwork, so I don't want to go through the steps...
  26. B

    Show that for a ferromagnetic material the field in the gap is given by?

    Homework Statement A toroidal shaped magnetic material of radius, a, and cross sectional radius R has a small transverse gap cut into it of length l. The toroid is uniformly overwound with a coil of N loops carrying a current I. Show that for a ferromagnetic material the field in the gap is...
  27. S

    Why is there a forbidden energy gap in solid state electronics?

    I am reading about solid state electronics(semiconductors). I've read that when atoms of many many atoms are brought close each other,as in a solid, the energy levels of energy states of different atoms get split up into different closely lying energy states collectively forming a band...
  28. M

    Fermi Energy level with respect to band gap energy

    Homework Statement Calculate Efi with respect to the center of the bandgap in silicon for t= 200, 400, 600 kelvin. Homework Equations ni = Nc e^-((Ec- Ef)/(kt)) k = boltzman constant t= temperature in kelvin Ec = energy level of the conduction band ef= fermi energy level ni=...
  29. S

    Calculating Energy Stored in a Capacitor with Varying Gap

    Homework Statement A capacitor is completely charged with 670 nC by a voltage source that had 200 V. What is its capacitance?==== 3.35×10-9 F 9(I got this y doing Q/V) The initial air gap of the capacitor above was 7 mm. What is the stored energy if the air gap is now 10 mm? Now...
  30. N

    Energy gap calculation for semi-conductors.

    Homework Statement Most solar radiation has a wavelength of 1 µm or less. (a) What energy gap should the material in a solar cell have if it is to absorb this radiation? (b) Is silicon an appropriate solar cell material? Explain your answer. Homework Equations f = c/lambda E =...
  31. Chronos

    What Causes Early Convective Instabilities in Supernova Explosions?

    Perhaps this explains the mass gap between neutron stars and stellar mass black holes. http://arxiv.org/abs/1110.1635 Missing Black Holes Unveil The Supernova Explosion Mechanism
  32. P

    Spark Gap & Current: Exploring the Impact on Circuits

    Does a spark gap increase the current in a circuit? My thinking is that the surrounding air is ionized and any "stripped" free electrons would add to the current.
  33. A

    Bridge Degree Between Electronics & Planetary Science?

    Does anyone here know of a possible bridge degree between a bachelor's deg in electronics engineering and a degree in planetary science? I plan to pursue degrees in astronomy and then planetary science without wasting my five years with electronics. Is it possible to link them? If so, what...
  34. S

    How to find the amount of inter record gap in a magnatic tape?

    hello i have a question given to me on a tutorial which is to find what is the largest IRG that will allow 80 percent of the tape to be data in 2400 foot magnetic tape has recording density 6400 Bpi and data records are 100 bytes and memory buffer is 10,000. i have been looking every where but i...
  35. Ivan Seeking

    News The wealth gap - 92% of Americans surveyed prefer Sweden over the US

    Take the test http://www.pbs.org/newshour/rundown/2011/08/wealth-how-does-the-us-slice-the-pie.html Video and text http://www.pbs.org/newshour/bb/business/july-dec11/makingsense_08-16.html Hopefully my point is obvious. When faced with the facts in terms easy to understand, most...
  36. B

    Cyclotron: Speed of Particle After 2nd Gap Crossing

    Homework Statement A cyclotron is a particle accelerator made of two electrodes shaped as two empty half-circles separated by a small gap. We consider the dees as lying on the x-y plane, having radius R, both with centre in the origin, and each occupying the semiplane of positive and...
  37. M

    Pseudogap and phonon gap. Does phonon (pseudo)gap exist?

    We all know that there exist pseudogap in superconductors and in metals (semimetals). Were there the experiments, aimed to find gaps analogues to pseudogap in phonon spectrum? Is pseudogap T* is connected with some change in phonon spectrum in some direction? The same question for...
  38. B

    Semiconductor quatum well find band gap question

    Hiya, been given this question which I am having problems with. Semi conductor quantum well structure contains a 100A thick layer of GaAs between thick AlGaAs layers. Find the band gap for the structure, where GaAs has the following parameters; conduction band effective mass 0.067 me, heavy...
  39. S

    3.5 FDD head size: size of the gap of the read/write heads

    3.5" FDD head size: size of the gap of the read/write heads I doubt anyone here knows the answer, but I thought I would ask anyway. I mean, I know not of a better forum on which to ask... Anyway, does anyone happen to know the size of the gap of the read/write heads of a 3.5" floppy disk...
  40. N

    The band gap discontinuity in DFT?

    The band gap discontinuity in DFT? Hi everybody... I've read about the band gap problem of Density functional theory, there is a discontinuity of the band gap when an electron add to the Kohn-Sham system I have two questions could anybody answer me? please 1- why this discontinuity happens...
  41. L

    Understanding Bandgap Voltage Reference Circuits

    I am not able to understand how a bandgap voltage reference works. The simplest ckt I found was here - (figure 2) - http://www.national.com/rap/Application/0,1570,24,00.html You have 2 branches of diodes, in one branch rich (high) current flows and in the other lean (small) current flows...
  42. L

    Energy gap from conductivity- temperature graph

    Homework Statement Hi, I have some values of conductivity in some temperatures. 0.01 at 400 Kelvin 10 at 600 K 70 at 700 K 1000 at 1000 K And I'm asked to find the energy gap of this intrinsic semi- conductor. Homework Equations The Attempt at a...
  43. D

    TiO2 Band Gap Energy: Direct vs. Indirect

    When we say generally TiO2 band gap energy, is it meaning direct or indirect band energy? Some papers show only direct BG or indirect BG or both. Is it right that one semiconductor has one of direct and indirect BG. I am a little bit confused.
  44. Q

    Energy band gap of semiconductors

    ok let's say i have a semiconductor like germanium with band gap of around 0.67eV at rtp. so this means that i need around 0.67 x 10-19 J of energy to cause valence electrons to jump to conduction band right? do i use the formula E = 1/2 kT to relate this energy to temperature? so i...
  45. T

    The Real Science Gap: An Overview

    http://www.miller-mccune.com/science/the-real-science-gap-16191/ Nothing Earth shattering to people in this group, but a nice summary of the problem.
  46. R

    Coulomb's gap and Wave Equation

    Hi all I was wondering if I could solve the schrodinger's equation to see the limiting velocity for a proton to tunnel through the coulomb gap in order for the first equation in the fusion reaction to occur Thanks a lot
  47. K

    Piecewise-linear ball complexes: calculations with GAP

    Dear all, Recently, some young people and I started a project that may be called "Piecewise-linear ball complexes: calculations with GAP". As to me, my direct aim is to make calculations in some TQFT's (topological quantum field theories) naturally defined on PL ball complexes of any...
  48. I

    Exploring Entropy Gap Expansion: Quantum or Universal?

    I'm asking this in the classical physics forums, because I view it as basically a thermodynamics question, but I'm wondering if I should put it in either the relativity or astrophysics forum, or even the quantum forum, because this topic is generally talked about in terms of cosmology...
  49. D

    Heat Transfer and Determining the Proper Gap

    I am struggling a bit with this problem: I have a pipe with a constant surface temperature of 1100F. I also have a tank which cannot reach a temperature higher than 258F. I am trying to figure out the minimum distance between the two (in 80F air, which will be moving at a minimum of 5 ft/sec)...
  50. P

    Physics Physics undergrad/grad gap year: ideas?

    One of our college's physics seniors scored poorly on the physics subject GRE and is looking for something to do for a year while s/he studies for, and retakes this test. Our student would like to find an appropriate position at a lab (academic, industrial, government...) which provides enough...
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