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A movable light emitting area by post-growth hydrogenation of a RT-LED. (a) Current-voltage I(V) characteristics of a virgin 200 μm diameter mesa RT-LED at T = 4.2 K. This is dominated by a strong resonance due to tunneling of electrons into the E1 QW subband and by much weaker resonances—observed in the conductance dI/dV—due to tunneling of holes into the HH1, LH1, and HH2 QW subbands; see inset for a sketch of the carrier injection into the QW. (b) Optical image of a 200 μm diameter mesa RT-LED. (c) and (d) Digital camera images of the EL emission intensity (at T = 9 K and V = 1.9 V) before [Virgin, (c)] and after [Hyd., (d) (Multimedia view)] post-growth hydrogen incorporation. The images were acquired with an 800 nm short-pass filter to remove the contribution from the GaAs spacer and contact layers. (e) Normalized EL maps for increasing values of the applied voltage, as obtained by plotting the EL intensity (atT = 9 K) around the QW emission energy (E = 1.63 eV). The dashed lines in the EL maps indicate the metal contact edge. The EL spatial profile is also shown for V = 1.84 V. [URL: http://dx.doi.org/10.1063/1.4844975.1]doi: 10.1063/1.4844975.1.
Properties of the movable RT-LED. (a) QW EL spectrum on the ring (position A in the EL map) and outside the ring (position B in the EL map) at a given applied voltage (V = 1.85 V). (b) Comparison of the bias dependence of the QW EL intensity in the hydrogenated sample (at the ring) and in the virgin sample (at the mesa center). In the virgin sample, the spatial inhomogeneity of the EL intensity is less than 4% and is independent on the applied voltage. (c) Position of the QW EL emission versus the applied voltage V: the light emitting area shifts linearly from the contact edge towards the mesa center. The continuous line is a linear fit to the data at V ≥ 1.8 V. (d) At a given position (r = 4.4 μm), the QW EL intensity versus the applied voltage shows a large peak-to-valley ratio (∼10), much larger than the peak-to-valley ratio (∼3) of the E1 peak in the current-voltage I(V) characteristics (see Fig. 1(a) ).
Modeling of the movable RT-LED. (a) Sketch of the spatial voltage drop along the mesa—r being the radial distance from the metal contact edge—induced by the hydrogen passivation of C-dopants in the p-type GaAs contact layer. This causes a spatial variation of the injection of carriers into the QW, with resonant injection occurring at a given position r *. (b) Dependence on r of the electron (d e) and hole (d h) tunneling distances and (c) of the tunneling voltages for the resonant injection of electrons (V E1) and holes (V HH1, V LH1, and V HH2) into the subbands of the QW. The simultaneous resonant injection of electrons and holes into the QW is highlighted by a red circle.
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