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Schematic diagram of voltage modulation of a vertical cavity transistor laser via intra-cavity photon-assisted tunneling.
Scanning electron microscopic image of a VCTL (cavity size in area 11 × 6 μm2). The VCTL is passivated with polyimide and is interconnected at emitter, base, and collector with metal vias.
(a) The collector output IC-VCE(IB) characteristics of a 11 × 6 μm2 VCTL (Fig. 2) showing the device operating at saturation (black), forward-biased active (red), and photon-assisted tunneling (blue background). The inset shows the electrical gain (ΔIC/ΔIB) as a function of base current at VCE = 4 and 5 V. (b) The optical output L-VCE(IB) characteristics show the emission intensity saturated at IB ∼ 6 mA, VCE = 3 V and starting to “roll off.” The blue background region shows a continuous decrease in light intensity due to intra-cavity photon-assisted tunneling occurring at the BC junction.
Spectra of a VCTL at IB = 1, 4, and 10 mA and VCE = 3 V, with the two major peaks separated by 0.37 nm at IB = 10 mA. The inset shows the extrapolation of L-IB. The threshold current is ITH ∼ 3.5 mA. For IB > 11 mA the signal level (peak amplitude) intensity saturates.
Spectra of a VCTL operating at constant base current IB = 14 mA with VCE = 1, 3, and 6 V, respectively.
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