We report p-doped long wavelength GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIP) grown by organometallic vapor phase epitaxy. The operation of these devices is based on the photocurrent induced through valence-band intersubband absorption by holes and, unlike n-doped QWIPs, can utilize normal incidence illumination. Carbon was used as the p-type dopant in a low-pressure (30 Torr) vertical-geometry reactor. The C-doped QWIPs consisted of fifty periods of 54-nm-thick undoped AlxGa1-xAs (x = 0.36 or 0.30) and C-doped GaAs wells (L(z) = 4 or 5 nm). Using normal incidence illumination, the C-doped QWIP with shorter wavelength response (x = 0.36, L(z) = 4 nm) exhibited a quantum efficiency of eta = 21.4% and a detectivity at the peak wavelength of D-lambda = 5.4 x 10(9) cm square-root Hz/W at 77 K. The peak and cutoff wavelengths were lambda-p = 8.1-mu-m and lambda-co = 8.9-mu-m, respectively. The C-doped QWIP with longer wavelength response (x = 0.30, L(z) = 5 nm) exhibited a normal incidence eta = 22.1% and D-lambda* = 3.5 x 10(8) cm square-root Hz/W for lambda-p = 10.5-mu-m (lambda-co = 11.7-mu-m). The detectivity of the C-doped QWIPs is about four times less than n-doped QWIPs for the same lambda-p but have the advantage of utilizing normal incidence illumination.
