The dark current and spectral photoresponse threshold of a semiconductor photodetector are normally determined by the minimum energy gap ( ) of the material, or the interfacial energy gap of the heterostructure. In this manuscript, we discuss the performance of an asymmetric p-GaAs/Al x Ga 1-x As heterostructure-based infrared photodetector, which shows an extended wavelength threshold beyond the limit set by . The measured dark current was found to agree well with fits obtained from a 3D carrier drift model using the designed value of ~0.40 eV (~3.1 µm). In contrast, the spectral photoresponse showed extended wavelength thresholds of ~68 µm, ~45 µm, and ~60 µm at positive, zero, and negative biases, respectively, at 5.3K. For a reference (symmetric) photodetector, the dark current was fitted with the designed value of ~0.30 eV, and excellent agreement was obtained for both the measured dark current and spectral response. This underlies the advantage of using asymmetric infrared photo-detector designs, in which an extension to the detected wavelengths can be obtained with little compromise to the dark current characteristics.
Abstract. Extension of the wavelength threshold of an infrared detector beyond λ t ¼ hc∕Δ is demonstrated, without reducing the minimum energy gap (Δ) of the material. Specifically, a photodetector designed with Δ ¼ 0.40 eV, and a corresponding λ t ¼ 3.1 μm, was shown to have an extended threshold of ∼45 μm at 5.3 K, at zero bias. Under negative and positive applied bias, this range was further extended to ∼60 and ∼68 μm, respectively, with the photoresponse becoming stronger at increased biases, but the spectral threshold remained relatively constant. The observed wavelength extension arises from an offset between the two potential barriers in the device. Without the offset, another detector with Δ ¼ 0.30 eV showed a photoresponse with the expected wavelength threshold of ∼4 μm.
We report the performance of a 30 period p-GaAs/Al x Ga 1Àx As heterojunction photovoltaic infrared detector, with graded barriers, operating in the 2-6 lm wavelength range. Implementation of a current blocking barrier increases the specific detectivity (D*) under dark conditions by two orders of magnitude to $1.9 Â 10 11 Jones at 2.7 lm, at 77 K. Furthermore, at zero bias, the resistance-area product (R 0 A) attains a value of $7.2 Â 10 8 X cm 2 , a five orders enhancement due to the current blocking barrier, with the responsivity reduced by only a factor of $1.5. Published by AIP Publishing.[http://dx.doi.org/10.1063/1.4952431] Infrared (IR) detectors and imaging systems are becoming increasingly important in a diverse range of military and civilian applications. In recent years, significant attention has been paid to incorporating current blocking architectures into detector designs. For example, AlGaAs current blocking layers have been utilized in quantum dot IR photodetectors (QDIPs) both to enhance performance [1][2][3][4][5][6] and to achieve elevated operating temperatures. [7][8][9] Similarly, in type II InAs/ GaSb superlattice (T2SL) IR photodetectors, majority carrier (hole) blocking layers have been implemented, 10 as well as electron blocking and hole blocking unipolar barriers in complementary barrier infrared detectors (CBIRD) 11 and p-type-intrinsic-n-type (PbIbN) photodiodes. 12 Furthermore, dark current suppressing structures were also demonstrated, such as conduction band barriers in nBn photodetectors 13,14 and XBn barrier photodetectors. 15 In general, the main goal in these architectures is to lower the dark current, but with a relatively small compromise to the photocurrent, thus achieving a significant improvement in the specific detectivity (D*).Due to the mature growth and established processing technology of p-GaAs/Al x Ga 1Àx As, these materials systems have become increasingly attractive for demonstrating heterojunction interfacial workfunction IR photodetectors (HEIWIP), 16 which operate up to room temperature. 17 Furthermore, replacing the constant Al x Ga 1Àx As barrier with a graded barrier, achieved by tuning the Al mole fraction (x), was found to enable photovoltaic operation as well. 18 This is advantageous over photoconductive operation as it offers thermal noise limited performance and reduced power consumption. In this letter, we report the effect of a current blocking barrier (CBB) on a 30 period p-GaAs/Al x Ga 1Àx As IR detector with graded barriers, which shows a photoresponse at 77 K in the $2-6 lm range under photovoltaic operation. We observe an approximately five orders of magnitude higher resistance-area product (R 0 A) at zero bias, resulting in a two orders of magnitude improvement in D*, with the responsivity compromised only by a factor of $1.5 at zero bias, compared to performance without the CBB.A p-GaAs/Al x Ga 1Àx As heterojunction IR detector was grown on a semi-insulating GaAs substrate by molecular beam epitaxy 19 ( Fig. 1(a)). The active region of the ph...
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