The design and characterization of strained-layer quantum well infrared photodetectors

Many different types of p-type strained-layer quantum well infrared photodetectors have been developed for normal incidence 3-5 {dollar}mu{dollar}m mid-wavelength infrared (MWIR) and 8-14 {dollar}mu{dollar}m long-wavelength infrared (LWIR) detection. The benefits possible in p-type QWIPs are: normal incidence detection without grating couplers, lower dark current and the ability to detect all incident infrared (IR) radiation polarizations.; The first p-type compressive strained layer (CSL-) QWIP is composed of InGaAs/AlGaAs and grown on semi-insulating (S.I.) (100) GaAs, which exhibits two-color two-band detection with an MWIR peak at 5.5 {dollar}mu{dollar}m and an LWIR peak at 7.4 {dollar}mu{dollar}m. The next p-type InGaAs/GaAs/AlGaAs CSL-QWIP uses a step-bound-to-miniband (SBTM) intersubband transition to detect IR radiation. This device was also grown on S.I. (100) GaAs and was found to have a peak detection wavelength at 10.4 {dollar}mu{dollar}m. The third p-type CSL-QWIP design consists of two highly strained InGaAs/AlGaAs multiquantum well stacks in series, separated by a common central ohmic contact. The MWIR stack showed two detection peaks at 4.8 and 5.4 {dollar}mu{dollar}m, while a 10.0 {dollar}mu{dollar}m peak was found for the LWIR stack.; The next p-type CSL design is called a superlattice infrared photodetector (SLIP) and consists of a radiation sensitive superlattice of 3 or more periods surrounded by a blocking barrier. The p-type CSL-SLIP was found to have a very long-wavelength infrared (VLWIR) detection peak at 19.2 {dollar}mu{dollar}m and was grown on S.I. (100) GaAs with InGaAs/GaAs/AlGaAs layers. A second p-type SLIP grown and characterized was an unstrained design which showed voltage tuning, with the detection peak of this SLIP shifts from 9.3 {dollar}mu{dollar}m to 6.5 {dollar}mu{dollar}m with the relative responsivity of the LWIR peak decreasing and the 6.5 {dollar}mu{dollar}m peak increasing with bias.; The final p-type QWIP investigated is the tensile strained-layer (TSL) InGaAs/InAlAs design grown on S.I. (100) InP which uses the light-hole to heavy-hole intersubband transition for detection. The TSL-QWIP was found to have a detection peak in the MWIR band at 5.2 {dollar}mu{dollar}m. As with all of the other strained and unstrained p-QWIPs, the device was found to be sensitive to normally incident IR radiation.; The broadband QWIPs (both n- and p-type) studied consist of three or four different quantum wells of varying thickness and composition combined in a unit cell separated by thick barriers. Each different quantum well is designed with a slightly different detection peak than an adjacent one, so that the individual spectra overlap to form a broader spectrum. These four devices were found to have detection peaks ranging from 9.3 to 10.3 {dollar}mu{dollar}m and spectral bandwidths of 21 to 63%.