We demonstrate an improvement in the operating temperature of a quantum dot-in-a-well (DWELL)-based infrared photodetector with spectral response observable till 250 K. This improvement was achieved through engineering the dot geometry and the quantum confinement via postgrowth capping of the quantum dots (QDs) by selecting overlying materials under various growth conditions. The effect of the capping procedures was determined by examining the optical properties of the QDs. These were then introduced into the active region of a DWELL IR photodetector. Using this approach, the dark current density is as low as 6.3 × 10-7 A/cm2 (Vb = 7 V) at 77 K; the highest operating temperature is increased to 250 K with the λp = 3.2 μm. The peak detectivity is found to be 1 × 109 cm·Hz1/2 /W at 77 K and 7.2 × 107 cm·Hz1/2/W at 250 K.