Abstract
We report on spectral investigation of photocurrent of a nonconventional GaAs/AlGaAs quantum well photodetector (QWP) which realizes a response to terahertz (THz) radiation by intradonor transitions (IDTs) in AlGaAs barriers rather than typical intersubband transitions (ISBTs) in GaAs wells. The photodetector shows dramatically enhanced photocurrent intensity and THz response when under a perpendicular magnetic field. This magnetic field helps to improve the absorption quantum efficiency, remove the restriction of the polarization selection rule, and extract high density electrons from two-dimensional electron gas in GaAs wells after electrons transfer into AlGaAs barriers. The effect of the magnetic field on the peak intensity and the linewidth of the photocurrent peak responses is exploited to distinguish IDT and ISBT and to identify the crucial role of electron transfer in THz detection in QWP. This work is useful for exploring detection strategy and technology for high responsivity THz photodetector.
Highlights
We proposed an alternative GaAs/AlGaAs quantum well photodetectors (QWPs), which displayed THz radiation response based on intradonor transitions (IDTs) from the 1s hydrogenic donor ground state to higher excited donor states in AlGaAs barriers ( 4 ) instead of intersubband transition (ISBT) from the ground to the excited subbands in GaAs wells ( 1 ), as shown in Fig. 1.2 Through the Landau quantization of in-plane electron motion which arises from a magnetic field B perpendicular to the epitaxial layer, electron transfer ( 3 ) begins to occur during the process ( 2 ) when the subband Landau level (LL) ε0,0 in GaAs wells approaches and surpasses the 1s hydrogenic donor ground level in AlGaAs barriers after B exceeds its threshold value B exceeds the threshold (Bt).[2,4,13,14,15,16]
The polarization selection rule which forbids the absorption of the light polarized perpendicular to the growth direction in the process of ISBT in GaAs wells is almost completely removed in IDT processes in AlGaAs barriers under strong magnetic field.[8,16]
The last point is the electron concentration participating in IDT processes in AlGaAs barriers can be as high as the 2DEG density of up to 3×1010 cm-2 in GaAs wells because these electrons are transferred from wells
Summary
GaAs-based terahertz (THz) quantum well photodetectors (QWPs) based on intersubband transition (ISBT) have attracted considerable attention in recent years due to their potential applications in various fields such as medicine, bio-sensing, and industrial inspection.[1,2,3,4,5] By adopting wellestablished quantum-well-infrared-photodetector (QWIP) structures, their operating wavelengths have been extended into THz region when the aluminum fractions in barriers of properly designed GaAs/AlGaAs QWPs were reduced.[4,6] the doping concentrations in GaAs wells have to be kept low and result in a relatively weaker ISBT absorption in THz QWPs due to many-particle effects in the two-dimensional electron gas (2DEG) in GaAs wells which impact negatively on the narrow ISBTs that principally determine the peak frequencies of THz QWPs.[7,8] This places the emerging solid-state THz technology at a disadvantage in application, especially when most THz sources are still suffering from weaker output power overwhelmed by high levels of thermal background radiation.[9,10,11,12].
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