High-Resolution X-ray Diffraction Analysis of p-Type Strained InGaAs/AlGaAs Multiple Quantum Well Structures
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INTRODUCTION
GaAs/AIGaAs multiple quantum well (MQW) material systems that allow infrared optical absorption have been attracted great attention in recent years. For n-type MQW, normalincidence intersubband optical transitions are possible for tilted ellipsoidal conduction-band minims, whereas for p-type MQW the allowed absorption of the normal incidence light result from mixing of the heavy- and light-hole states of the valence band. The p-type GaAs/AlGaAs MQW structures have other preferable properties for quantum well infrared photodetectors (QWIPs). First, the large effective mass of holes permits the use of much higher doping levels and, consequently, the possibility of larger optical absorption coefficients than that for n-type QWIPs, without the concomitant rapid increase of the thermionic and tunneling components of the dark current. Second, GaAs/AIGaAs MQW systems are at present preferable to 11-VI materials, not only because of the mature technology in 1II-V compound semiconductor, but also because of their potential application for monolithic integration of the photodetector with highspeed GaAs-based electronics. There have been several theoretical [1,2,3] and experimental [4,5,6] research reports on the physics and application of normal-incidence long-wavelength intersubband optical transitions in different p-type material systems to QWIPs. Recently, the strained material systems have been proven to be highly interested for both fundamental physics [7,8] and for applications [9] because of the possibility of designing the valence band structure as a function of strain [10]. The use of intentionally strained heterostructures has greatly enhanced the performance of electrical and electro-optical semiconductor devices [11]. Among them, the p-type strained InGaAs/AIGaAs multiple quantum well material combination becomes particularly important for device applications in the near and far infrared wavelength range. Chu
229 Mat. Res. Soc. Symp. Proc. Vol. 607 © 2000 Materials Research Society
and Li [12] have studied strained p-type QWIPs of InGaAs/GaAs, InGaAs/AlGaAs, and InGaAs/AlGaAs-GaAs, and reported their superior detectivity over the unstrained p-type QWIPs. We recently reported the optical properties and I-V characteristics of the p-doped Ino.isGao.85As/Alo. 45Gao. 55As multiple quantum well (MQW) structures, designed for detection of long wavelength infrared (LWIR) around 10 pm [13]. The dark current of the QWIPs was found two orders of magnitude less than that of GaAs/AlGaAs QWLPs. So far, there is still little report on the effects of p-doping level on the properties of quantum well structures. High-resolution x-ray diffraction (HRXRD) is a powerful tool with which to characterize semiconductor superlattice (SL) [14,15,16,17]. The information, such as the periodicity and mean mismatch, which are essential to the structure, can be straightforwardly obtained. And also the intensity and the peak line width of the diffraction Bragg peaks are a good indicator of the quality of the MQW, such as the cry
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