Short wavelength Infrared (SWIR) focal plane arrays (FPAs) working at room temperature have many important military and cosmonaufic applications. The dimensions of detectors in FPAs have gradually been reduced. The problem of the increase of the effective photoactive area in photovoltaic detectors by conventional technology become more obvious. Planar InGaAs (PIN) linear detector at 300K using laser beam induced currernt (LBIC) was measured. From the results, the increase of the effective optically sensitive area exits. The landscape orientation diffusion of the dopant and the sidecollecting of minority carriers are the two main reasons for the increase of the effective photoactive area for the planar InGaAs linear detector. It is important to the research and design of linear and twodimensional InGaAs focal plane arrays (FPAs).