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4. [3.23] Experiments carried out on various direct bandgap semiconductor LEDs give the output spectral linewidth (between half intensity points as in listed in Table 3.5. From Figure 3.31 we know that a spread in the wavelength is related to a spread in the photon energy AAS (he Eph)AEph , where Eph-huis the photon energy. Suppose that we write Eph-hoa and AEph-A(hu) mk BT where m is a numerical constant. Therefore, Άλ (mksThce By appropriately plotting the data in Tabk 3.5, and assuming T-300 K, find m. Table 3.6 gives the linewidth Δλ 2 for various visible LEDs based on GaAsP. Radiative recombination is obtained by appropriately doping the material. Using m-3.0 in Eq. (I), T 300 K, calcuate the expected spectral width for each and compare with the experimental value. What is your conclusion? Table 3.6 Linewidth Ada between half points in the output spectrum (intensity vs wavelength) of various visible LEDs using GaAsP Peak wavelength f emission () am 6 635 28 36 40 Color GreenYew Orange Red GaP(N GaAsPIN) GaAs (N) GaAsP Table 3.5 Linewidth Adia between half points in the output spectrum (intensity vs. wavelength) of four LEDs using direct bandgap semiconductors Peak wavelength of emission (2) nm 650 810 820 890 1270 1500 950 1150 110 150 36 40 90 A nm Material (Direct E) AlGaAs AlGaAs AlGaAs GaAsGaAs InGaAsP InGaAsP InGaAsP

Answer 1

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