Photocurrent enhancement of superlattice infrared photodetector (SLIP) is demonstrated using SL sandwiched between front (thin) and rear (thick) barriers. These two barriers are utilized for photoexcited electrons in second miniband oscillate between them and punch through the front barrier to enhance tunneling probability. However, the supply of electrons is limited by the thick barrier and thus we need to fabricate the emitter contact on the SL. The experimental results of this SLIP shows higher responsivity at low bias (0.15 V, 0.20 V and 0.25 V) and one-order higher associated detectivity (1.2 × 1010 cmHz1/2/W, at 80 K) than conventional single-barrier SLIP. Due to better performance at low bias, this SLIP is suitable for low power consumption applications.
We have designed a double-barrier superlattice infrared photodetector (SLIP) which has a superlattice (SL) sandwiched between the thin and thick barriers. Photoelectrons can bounce back and forth between the two barriers and inject through the thin barrier to enhance the photocurrent. However, the supply of electrons is limited by the thick barrier and thus we have to fabricate the emitter contact on the SL. In comparison with the single-barrier SLIP, this structure shows at least one-order higher magnitude of photocurrent at low bias and the associated detectivity is also increased for more than one order. The dramatic increment of the photocurrent is consistent with our design in the detailed analysis. Because it has the optimized performance at low bias, this double-barrier SLIP is suitable for low power consumption applications. Our detector can be operated at 100 K by blocking barriers incorporated into the structure to reduce the dark current.
Infrared (IR) detectors play a critical role in both military and civilian applications and have been widely researched in recent decade. Because the atmospheric transparent windows for the IR radiation exist within the spectral ranges of 3−5 and 8−12 μm, and the spectrum of the black-body radiation at room temperature has a peak at 10 μm, the detectors with the 8-12 μm detection spectra are helpful to identify the heat radiation from a target at room temperature. Such detectors are the research focus in this chapter. The employment of intersubband transitions for the infrared radiation detection has drawn much attention. The transition is completed by the electrons which absorb photons with the appropriate energy equal to the suband energy difference to transit from the low subband to the high one. The intersubband photodetectors can be made from semiconductor heterostructures of multiple quantum wells (West & Eglash, 1985) (Harwit & Harris Jr., 1987) ( Levine et al., 1987) or superlattices as shown in Fig. 1. Infrared detection will be done by the intersubband transitions between two quantum states in the multiple quantum wells or two minibands in the superlattices. The wells are sandwiched by thick barriers in the multiple quantum well structure. Therefore electron wavefunctions in the wells would not interact with each others and discrete quantum states are formed. Contrarily, the adjacent wells in the superlattice are separated by thin barriers. Minibands are formed in the superlattice region by the coupling of electron wavefunctions. As shown in Fig. 1, in comparison with the quantum well infrared photodetectors (QWIPs), superlattice infrared photodetectors (SLIPs) have three different characteristics. The first one is the low operational bias. The electrons in the miniband of the superlattice (SL) are conductive while those in the quantum states of the multiple quantum wells (MQWs) are confined. The SL hence becomes a low resistance structure and thus no externally applied bias drops on the SL under low bias range. Therefore, the current blocking layer is needed to decrease the dark current in SLIPs and can determine the operational bias range. 6
An infrared photodetector using the structure of a 15-period superlattice (SL) integrated with 50-period multiple quantum wells (MQWs) is investigated. The MQWs are utilized to reduce the noise current power and to add the response range. From the results of current ratio and response, the photocurrent of the SL is not reduced by the additional MQWs but the dark current is. Hence, due to the low noise gain and low dark current, the maximum detectivity (D * ) can occur at low negative bias. In addition, the photovoltaic response even appears at 80 K. It is observed that the photoelectron transport directions from the SL and the MQWs are opposite under zero bias. In comparison with the SL with a single barrier, this structure also demonstrates the higher photocurrent and lower dark current. From our experimental results, this structure is appropriate for the operation at low bias and high temperature. However, the tradeoff is the small operational voltage range
A double-barrier superlattice infrared photodetector (SLIP) that contains a superlattice sandwiched by the thin and thick barriers has been developed. Photoelectrons can bounce back and forth between the two barriers and inject through the thin barrier to enhance the photocurrent. In comparison with the single-barrier SLIP, this structure shows at least one-order higher magnitude of photocurrent at low bias and the associated 80 K detectivity is also increased for more than one order. This detector also shows high-temperature operation above 100 K with an appropriate detectivity at low bias (1.1 × 10 9 cm Hz 1/2 /W at 0.17 V). A simple photoelectron resonance model is given to analyze the resonance phenomenon. It is found that photoelectrons excited by 9.2 µm wavelength can resonate in the bottom of the second miniband by 42 to 49 times from 0.05 to 0.15 V to enhance the photocurrent dramatically.
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