Figure 1

Schematic potential-energy profile felt by a photogenerated electron tunneling through an undoped semiconductor superlattice of miniband width $\Delta$, in the low-electric (a) and high-electric (b) field limits when the field is perpendicular to the superlattice’s material interfaces. The electrons are pumped from the valence to the conduction band by photons whose energy lies between the band gaps of the two semiconductors making the superlattice.Reuse & Permissions

Figure 2

Experimental $2eI$ (solid line) and noise (connected circles) photocurrent characteristics at $T=6\mathrm{K}$ of three $p-i-n$ GaAs-GaAlAs heterojunctions with a superlattice in their intrinsic regions. The junctions differ only in the well/barrier thickness of their superlattices. The current maxima (denoted by $n=-1,-2$) correspond to resonant absorption involving Stark-ladder states in the conduction band. In (a) and (b), corresponding to a $4.0/1.5\mathrm{nm}$ superlattice, for voltages larger than $-0.5\mathrm{V}$, the experimental shot noise is much smaller than the Poissonian value ($2eI$), whereas for smaller voltages the two values are practically the same, regardless of the excitation wavelength. The noise reduction was much less pronounced in a $4.0/2.0\mathrm{nm}$ structure, (c), and was absent in a $5.0/3.5\mathrm{nm}$ structure, (d).Reuse & Permissions

Figure 3

Experimental Fano factor as a function of electric field, for five superlattices with the same well width (4.0 nm) and barrier widths ranging from 1.5 to 4.0 nm. (We show data for two superlattices with 1.5 nm barrier width that were grown several months apart from each other.) At moderately high fields ($>80\mathrm{kV}/\mathrm{cm}$) $F\approx 1$ for all superlattices. At low fields $F$ is the smaller, the narrower the barrier width, with the exception of the $4.0/4.0\mathrm{nm}$ heterostructure. A semiclassical multibarrier model predicts a low-field value of $F=1/3$, independent of the barrier width, and a gradual increase toward $F=1$ at very high fields, as shown in (b), where we summarize the calculated dependence of the Fano factor on electric field for three superlattices with the same 4.0 nm well width and different barrier widths: 1.5, 3.0, or 4.0 nm.Reuse & Permissions