Study of MOCVD-grown heavily carbon-doped P-type normal incidence sensitive GaAs/AlGaAs MQW mid-infrared photodetectors and N-type MQW photodetectors
Abstract
Normal-incidence (NI) sensitive infrared (IR) photodetectors are attractive because they are suitable for two-dimensional focal plane array applications P-type GaAs/AlGaAs multiple quantum wells (MQWs), unlike n-type MQWs, are sensitive to NI light due to the coupling between the light and heavy hole bands. This thesis presents the first experimental investigation of heavily doped p-type MQWs, which are capable of strong absorption, and their application to IR photodetectors. A new mid-IR wavelength range (2.1-2.4 mum) absorption is observed and explained. Based on a three-band calculation model, the origin of the new mid-IR absorption is identified as intersubband absorption transitions between the heavy and light hole ground states (HH1 & LH1) and first excited spin-orbit-split-off state (SO2). The characteristics of photodetectors made on the heavily doped p-type MQW structure is studied. A NI photoresponse at 2.1 mum, which is the shortest wavelength reported for any MQW IR photodetectors, is obtained. The detector shows symmetric I-V characteristics and a relatively low dark current which is attributed to the large hole effective mass and the effects of many-body interactions. The detector has a detectivity of 1.9 × 10sp{10} cmsurdHz/W at 77 K, which is similar to that of other reported MQW mid-IR photodetectors, and a background limited photocurrent (BLIP) temperature of ∼100 K. The result indicates that the HH1-SO2 & LH1-SO2 absorption transitions are useful transitions for mid-IR wavelength photodetector applications. This result provides a new way of making NI sensitive multi-color photodetectors to cover a broad wavelength range. Long-IR wavelength (7-9 mum) absorption was observed in the heavily doped p-type MQW structures and is analyzed using an existing two-band theoretical calculation model. Good agreement between the experimental and theoretical results indicates that carrier-carrier interactions (many-body effects) are indispensable in determining eigenstates and optical properties of heavily doped p-type MQWs. The Metalorganic Chemical Vapor Deposition (MOCVD) technique was used to grow state-of-the-art GaAs/AlGaAs MQW structures: n-type and heavily doped p-type as well as undoped (UD). Interface roughness and layer thickness repeatability of one atomic layer are demonstrated, for the first time, for the MOCVD grown UD-MQWs with QWs as thin as 14 A. Various growth schemes were developed to grow high quality well-region-doped MQWs. A n-type MQW (doped at 2.4 × 10sp{18} cmsp{-3}) with an internal intersubband absorption quantum efficiency of 15% is achieved, which is comparable to the best reported results of n-type MQWs grown by the molecular beam epitaxy technique. For the first time, p-type MQWs with doping concentrations as high as 5 × 10sp{19} cmsp{-3} and with well-controlled and abrupt doping profiles are achieved with the MOCVD technique using carbon as the p-type dopant.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- September 1997
- Bibcode:
- 1997PhDT.......204M