| Terahertz wave has not yet been fully explored but must have brightprospects. Originating from intersubband transition, THz quantum wellphotodetector (THz QWP) has some unique advantages, such as fast responsespeed and the flexibility that can be designed according to a requiredresponse frequency.In the first part of this paper, some works about design of THz QWP aregiven. First, the doping concentration is usually low, so some approximationformulas for IR QWP are not applicable. The condition of optimal dopingconcentration for maximizing dark current limited detectivity D*detisdeduced when QWP is lightly-doped. In addition, many body effects are thekey factors which have to be considered when design THz QWPs. Theiteration method to self-consistently solve QWP’s band structure is presentedand plane wave expansion is employed to do numerical simulation. Moreover, depolarization effect is also considered to reform the calculation results ofpeak frequency. Afterwards, when doping concentration is fixed, the QWPs’parameters which meet the requirement of making first excited subband inalignment with the top of the barrier (ΔE≈0) are given with considering manybody effects. At last, when doping concentration is selected by the conditionwhich maximize D*det, the QWPs’ parameters which meet ΔE≈0are givenwith considering many body effects.In the second part of this paper, two schemes for improving operationtemperature are proposed. The first is to incorporate an optical antenna whichfocuses incident THz wave. Numerical results show that the QWP with peakfrequency higher than5.5THz is expected to achievebackground-noise-limited performance (BLIP) at77K or above whenemploying a106times enhancement antenna. The second scheme is to use alaser as the signal source to achieve photon-noise-limited performance (PLIP)at high temperatures. Simulations show that when operating below criticaltemperature QWPs in the range of1~7THz can reach PLIP under practicalillumination intensities. |
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