The effect of energy band control with varying carrier concentration in GaAsSb-based backward diodes was investigated and diode parameters were analyzed to enhance voltage sensitivity. The backward diodes consisted of a heterojunction of p-GaAs0.51Sb0.49/i-In0.52Al0.48As/n-In0.63Ga0.37As/n-In0.53Ga0.47As, and they were mostly lattice-matched to an InP substrate. The degree of energy band bending at the depletion layer in n-In0.63Ga0.37As was varied on the basis of the carrier concentration in the n-In0.53Ga0.47As band control layer. Voltage sensitivity depends on carrier concentration since the concentration affects the band bending structure at the junction. The parameter analysis indicated that junction capacitance decreased when the carrier concentration in the band control layer decreased. When the carrier concentration in the band control layer was as low as 5×1018 cm-3, with the diode mesa at a diameter of 2.0 µm, an unmatched voltage sensitivity of 1495 V/W was obtained.