Negative differential conductance in interband cascade emitters

We report a detailed examination of multiple negative differential conductance (NDC) features with hysteresis, observed in interband cascade lasers and light emitting diodes made from six different wafers covering an emission wavelength range from 2.7 to about 7 μm. These features arise from resonant tunneling in quantum wells (QWs), can be observed in both forward and reverse biases, and persist up to 160 K and over 300 K, respectively. By comparing features from wafers with a variable number of cascade stages (Ns) and different electron injector doping concentrations, strong correlations are established between the Ns and the number of NDC peaks, as well as between the appearance of forward-bias NDC features and the doping concentration. Under reverse bias, two distinct groupings of NDC peaks appear, which can be plausibly attributed to resonant tunneling through both ground and excited states in QWs. By comparing different internal structures, this tunneling can be isolated to the cascade stages of the emitters. NDC analysis is also shown to be useful as a tool for diagnosing partial internal damage within devices, providing a simple non-destructive way to test device performance.