Influence of potential fluctuations on electrical transport and optical properties in modulation-dopedGaN/Al0.28

Comment on “Fermi-edge singularity observed in a modulation-doped AlGaN/GaN heterostructure” [Appl. Phys. Lett. 73, 2471 (1998)]

“…We find their interpretation surprising, in view of our own earlier results. 3,4 As illustrated in a schematic band diagram in Fig. 1, the PL emission related to electrons in the twodimensional electron gas ͑2DEG͒ recombining with free or localized holes is expected to occur below the GaN band-gap energy, as typically found in earlier work on this material system, 3,4 as well as in other systems like InGaAs/InP and AlGaAs/GaAs.…”

“…3,4 As illustrated in a schematic band diagram in Fig. 1, the PL emission related to electrons in the twodimensional electron gas ͑2DEG͒ recombining with free or localized holes is expected to occur below the GaN band-gap energy, as typically found in earlier work on this material system, 3,4 as well as in other systems like InGaAs/InP and AlGaAs/GaAs. 2,5,6 The bandbending caused by the 2DEG typically reduces the PL recombination energy more than the increase due to confinement in the interface notch.…”

“…In fact, this broad PL spectrum is at an energy where the Al 0.09 Ga 0.91 N barrier is expected to give a near-band-gap PL spectrum, as also typically observed previously in such structures. 3,4 The large width of the PL emission could be a sign of a high trap density of the barrier material. The temperature dependence observed in Fig.…”

Radiative recombination in In0.15Ga0.85N/GaN multiple quantum well structures

“…A fluctuating field of the order 100 V/cm in the QW plane would thus be sufficient for impact excitation of excitons, provided energetic carriers are present in the initial relaxation process. In reality these fluctuating fields are much larger, of the order 10 3 -10 5 V/cm, depending on the lateral extent of the short range localization potentials [31]. Already a random distribution of donors at a total residual density of 10 17 cm -3 is sufficient to cause local fields of the order kV/cm in the QW plane.…”