In this letter we introduce a quantum well infrared photodetector (QWIP) structure, which we refer to as the quantum grid infrared photodetector (QGIP). In an ideal structure, a grid pattern with very narrow linewidth is created in the QWIP active region to achieve lateral electron confinement, thereby improving its absorption as well as transport characteristics. In order to realize this detector structure, we have fabricated QGIPs with line patterns of lithographical linewidths wl ranging from 0.1 to 4 μm, allowing for possible sidewall depletion. Low-damage reactive ion beam etching was employed to produce vertical sidewalls. From the experimental data, although the best detector performance occurs at wl ≈ 1.5 μm, the detector starts to improve when wl<0.5 μm, indicating a possible quantum confinement effect. © 1999 American Institute of Physics.