Question

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, AM(hc EAEph , where Eph = hv is the photon energy. Suppose that we write Eph hc/ and AEph A(hu) mkBT where m is a numerical constant. Therefore, A (mk3T/hc) By appropriately plotting the data in Table 3.5, and assuming T = 300 K, find m. Table 3.6 gives the linewidth AM12 for various visible LED8 based on GaAsP. Radiative recombination is obtained by appropriately doping the material. Using m = 3.0 in Eq. (1), T= 300 K, calculate the expected spectral width for each and compare with the experimental value. What is your conclusion? = Table 3.5 Linewidth A212 between half points in the output spectrum (intensity vs. wavelength) of four LEDS using direct bandgap semiconductors Peak wavelength of emission (A) nm 950 650 810 820 890 1150 1270 1500 22 36 40 50 55 90 110 150 Δλιη nm Material (Direct Eg) AlGaAs AlGaAs AlGaAs GaAs GaAs InGaAsP INGAASP InGaAsP Table 3.6 Linewidth AAn between half points in the output spectrum (intensity vs. wavelength) of various visible LEDS using GaAsP Peak wavelength of emission (A) nm 565 583 600 635 28 36 40 40 Ali1/2 nm Color Yellow Red Green Orange GaP(N GaAs (N Material GaAsP(N GaAsP

Answer 1

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