Figures

Figure 1

Schematic of the structures of the GaN/InGaN p-i-n samples used in this study.

Figure 2

Calculated bandstructures for the three samples studied in this work. This figure shows the directions of the built-in electric field, Ebi, and the piezoelectric electric field, Epiezo. Notice that the piezoelectric field within the quantum well opposes the built-in electric field.

Figure 3

Time-integrated photoluminescence set-up. The frequency doubled output of a femtosecond Ti:Sapphire laser is used as the pump source. Standard lock-in techniques are used to improve signal to noise ratio. The samples were edge emitting due to the waveguiding of the GaN buffer layers.

Figure 4

Time-integrated photoluminescence for sample B2. In this case, the frequency doubled output of the femtosecond Ti:Sapphire laser is tuned to 370 nm. Clearly, excitonic emission centered at 450 nm is present. In addition, sufficient overlap of the pump wavelength and the absorption edge of GaN was present. The yellow emission is from Ga vacancies within the n-doped material and served as a marker for the presence of carriers for screening of the built-in electric field.

Figure 5

Time-integrated photoluminescence for sample B10 with the pump tuned to 370 nm. Clearly, excitonic emission centered at 411 nm is present. Again, the yellow emission is clearly visible, however excitonic emission dominates at a lower fluence.<

Figure 6

Time-integrated photoluminescence for sample B20 with the pump tuned to 370 nm. Excitonic emission was centered at 424 nm. The yellow emission is still present but less than that of the previous two samples.

Figure 7

Time-integrated photoluminescence for all three samples for the same fluence. In this case, the frequency doubled output of a femtosecond Ti:Sapphire laser was tuned to 400 nm. This pump wavelength was sufficiently long to be absorbed only by the quantum well material. As expected, the PL intensity is proportional to the total length of the quantum wells within the intrinsic region. There was no evidence of yellow emission for the carrier densities excited with the given fluence at 400 nm.

Figure 8

Time-resolved photoluminescence using a Hamamatsu C4334 streak camera. As in the time-integrated photoluminescence, the frequency doubled output of a femtosecond Ti:Sapphire laser is used as the pump source. The streak camera is triggered synchronously with the pulses from the Ti:Sapphire.

Figure 9

Calculated excitonic transition energies and shift of excitonic transition energy versus in-well field for samples B10 and B20 for conduction band offsets varying from 0.6 to 0.8.

Figure 10

Time-resolved photoluminescence spectra for sample B10 at 15K with pump power of 12 mW and pump wavelength of 375 nm. There is an observed shift of ~10 meV.

Figure 11

Time-resolved photoluminescence spectra for sample B20 at 15K with pump power of 12 mW and pump wavelength of 386 nm. There is an observed shift of ~30 meV.

Figure 12

Temporal resolution of emission lifetimes for different emission energies for sample B20. The high energy emission is the expected emission with no in-well field. Notice that the lifetime is significantly shorter.

© 1999 The Materials Research Society