We report on negative differential photovoltage (DPV), which is observed under modulated photoexcitation of a double heterojunction, when the common positive photovoltage increment due to photocurrent modulation is suppressed by high bias current. The negative DPV was shown to be due to the effect of photoconductivity on the series resistance of the heterojunction and due to the modulation of junction temperature. In AlGaInP double heterojunction light-emitting diodes, the magnitudes of negative DPV in the range of −10 μV correspond to the estimated variation of series resistance and junction temperature as low as ∼10−3 Ω and ∼10−2 K, respectively.

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We report on the nonmonotonous variation of photoelectrical properties of commercial AlGaInP LEDs during the aging process. The light-generated current and short-circuit photocurrent were found to drop by the factors of 2 and 1.5, respectively, after about 3 h of aging at the rated forward current of 1400 mA with subsequent recovery and stabilization within ∼1000 h of aging. The temporal minima of photocurrents were accompanied by increased photoconductivity revealed from the negative differential photovoltage under modulated photoexcitation as well as by the minimum of optical output and the maximum of the ideality factor of the LEDs at low forward currents. The observed temporal variation of the photoelectrical properties was attributed to the interplay of recombinationenhanced growth and annealing of defects responsible for nonradiative recombination and photoconductivity in the active and cladding layers of the LEDs, respectively.