FLORIDA UNIV GAINESVILLE DEPT OF ELECTRICAL ENGINEERING
During this reporting period 02-01-94 to 04-30-94 we have continued to make excellent progress. We report two new normal incidence p-type strained- layer III-V quantun well infrared photodetectors QWIPs for 3-5 and 8-14 um detection. An ultra-low dark current p-type tensile strained-layer PTSL In0. 3Ga0.7AsIn0.52Al0.48As QWIP grown on InP by MBE for 8-14 um detection has been developed. It shows BLIP for T100 K. Due to a 1.5 lattice mismatch between the substrate and quantum well, a biaxial tensile strain was created in the well layers. As a result, the light-hole state becomes the ground state for the free hole with small effective mass. The dramatic increase of optical absorption can be attributed to the large in-plane density of states and small light-hole effective mass due to the heavy- and light-hole state inversion. The BLIP detectivity for the PTSL-QWIP was found to be 5.9xl0exp 10 Jones at 8.1 um, V sub b 2V, and T 77 K. A new p-type compressive strained-layer PCSL In0.4Ga0.6AsGaAs QWIP grown on GaAs substrate for 3-5 and 8-14 um has also been developed for the first time. This PCSL-QWIP shows a double-peak response between 8 and 9 um wavelength by utilizing the resonant transport coupling mechanism between the heavy-hole type-I states and the light-hole type-II states. Using the compressive strain in the quantum well, normal incident absorption was greatly enhanced by the reduction of heavy-hole effective mass and the increase in the offzone center density of states. Detectivity at 8.9 um was found to be 4.0x10exp 9 Jones at V sub b 0.3 V and T 75 K for this PCSL-QWIP.