基于锑化物二类超晶格的多色红外探测器研究进展

近年来InAs/GaSb二类超晶格红外探测器在材料晶体结构生长、器件结构设计与成像应用方面取得了飞速发展。尤其在多色红外探测方面,二类超晶格材料以其具备的带隙可调、暗电流小、量子效率高、材料均匀性高,以及成本低等优越性能,使其逐步成为第三代红外焦平面探测器的优选材料。本文阐述了锑化物窄带隙半导体研究中心的锑化物多色红外探测器研究进展。本团队成功实现了低噪声、高量子效率以及低光学串扰的短/中、短/长、中/长、长/长、中/长/甚长波等多种高性能多色红外探测器研制。     

Investigation of active-region doping on InAs/GaSb long wave infrared detectors

The eight-band κ·p model is used to establish the energy band structure model of the type-II InAs/GaSb superlattice detectors with a cut-off wavelength of 10.5μm,and the best composition of M-structure in this type of device is calculated theoretically.In addition,we have also experimented on the devices designed with the best performance to investigate the effect of the active region p-type doping temperature on the quantum efficiency of the device.The results show that the modest active region doping temperature(Be:760℃)can improve the quantum efficiency of the device with the best performance,while excessive doping(Be:>760℃)is not conducive to improving the photo response.With the best designed structure and an appropriate doping concentration,a maximum quantum efficiency of 45% is achieved with a resistance-area product of 688?·cm^2,corresponding to a maximum detectivity of 7.35×10^11cm·Hz^1/2/W.     

锑化物超晶格长波红外焦平面探测器研究进展

锑化物的研究开始于20世纪50年代,70年代随着超晶格概念及后来能带工程的出现,锑化物在红外探测领域的潜力逐渐显露.基于现实的需求,锑化物材料的生长外延及工艺处理技术取得了快速进步,这也得益于之前对Ⅲ-Ⅴ族材料的大量研究.Ⅱ类超晶格(T2SL)的发展主要源于两个主要原因:首先相对于HgCdTe材料,Ⅱ类超晶格具有低成本、可重复性、可操作性、高均匀性等优势,尤其在长波红外及以上波段,Ⅱ类超晶格相对于HgCdTe的优势更明显.其次与HgCdTe材料相比,Ⅱ类超晶格具有很低的俄歇复合概率,这意味着Ⅱ类超晶格红外探测器具有比HgCdTe探测器更低的暗电流或更高的工作温度,提高长波焦平面的工作温度对于降低成像系统的功耗、尺寸及重量至关重要.另外,大气窗口在8–14μm有最高的透射率,同时温度为室温(300 K)的物体所发射的红外辐射波长大约为10μm.因此,长波红外探测对于InAs/GaSbⅡ类超晶格极具价值.理论上Ⅱ类超晶格红外探测器在等效截止波长下能提供同等或超越HgCdTe探测器的性能.但由于Ⅱ类超晶格材料在少子寿命上与HgCdTe存在很大差距,导致Ⅱ类超晶格探测器在耗尽区有很高的产生复合电流.为了抑制产生复合电流及其他机制暗电流,提出了各种结构并应用于Ⅱ类超晶红外探测器上,如PπMN结构、CBIRD以及单极势垒型等,极大地降低了长波器件的暗电流,同时增加了器件阻抗及探测率.此外,InAs/InAsSb超晶格的提出,避免了由Ga在禁带引入复合中心,有效地提高了少子寿命.随着Ⅱ类超晶格技术及理论的不断完善,锑化物超晶格长波焦平面在可操作性、均匀性、稳定性、可扩展性上的优势将更为明显.     

Wet etching and passivation of GaSb-based very long wavelength infrared detectors

The etching and passivation processes of very long wavelength infrared (VLWIR) detector based on the InAs/GaSb/AlSb type-II superlattice have been studied. By studying the effect of each component in the citric acid solution (citric acid, phosphoric acid, hydrogen peroxide, deionized water), the best solution ratio is obtained. After comparing different passivation materials such as sulfide + SiO₂, Al₂O₃, Si₃N₄ and SU8, it is found that SU8 passivation can reduce the dark current of the device to a greater degree. Combining this wet etching and SU8 passivation, the R₀A of VLWIR detector with a mesa diameter of 500 μm is about 3.6 Ω ·cm² at 77 K.     

Very long wavelength infrared focal plane arrays with 50% cutoff wavelength based on type-Ⅱ In As/GaSb superlattice

A very long wavelength infrared(VLWIR) focal plane array based on In As/Ga Sb type-Ⅱ super-lattices is demonstrated on a Ga Sb substrate. A hetero-structure photodiode was grown with a 50% cut-off wavelength of 15.2 μm, at 77 K.A 320×256 VLWIR focal plane array with this design was fabricated and characterized. The peak quantum efficiency without an antireflective coating was 25.74% at the reverse bias voltage of-20 mV, yielding a peak specific detectivity of 5.89×1010cm·Hz~(1/2)·W~(-1). The operability and the uniformity of response were 89% and 83.17%. The noise-equivalent temperature difference at 65 K exhibited a minimum at 21.4 mK, corresponding to an average value of 56.3 mK.     

Growth of high material quality InAs/GaSb type-II superlattice for long-wavelength infrared range by molecular beam epitaxy

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.     

Performance of dual-band short-or mid-wavelength infrared photodetectors based on InGaAsSb bulk materials and InAs/GaSb superlattices

In this paper,we demonstrate bias-selectable dual-band short-or mid-wavelength infrared photodetectors based on In_(0.24)Ga_(0.76)As_(0.21)Sb_(0.79)bulk materials and InAs/GaSb type-II superlattices with cutoff wavelengths of 2.2μm and 3.6μm,respectively.At 200 K,the short-wave channel exhibits a peak quantum efficiency of 42%and a dark current density of5.93×10~(-5)A/cm~2at 500 mV,thereby providing a detectivity of 1.55×10~(11)cm·Hz~(1/2)/W.The mid-wave channel exhibits a peak quantum efficiency of 31%and a dark current density of 1.22×10~(-3)A/cm~2at-300 mV,thereby resulting in a detectivity of 2.71×10~(10)cm·Hz~(1/2)/W.Moreover,we discuss the band alignment and spectral cross-talk of the dual-band n-i-p-p-i-n structure.     

Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

In this paper we focused on the mask technology of inductively coupled plasma(ICP) etching for the mesa fabrication of infrared focal plane arrays(FPA).By using the SiO_2 mask,the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls.Comparing the IV characterization of detectors by using two different masks,the detector using the SiO_2 hard mask has the R_0A of 9.7×10~6 Ω·cm~2,while the detector using the photoresist mask has the R_0A of3.2 × 10~2 Ω·cm~2 in 77 K.After that we focused on the method of removing the remaining SiO_2 after mesa etching.The dry ICP etching and chemical buffer oxide etcher(BOE) based on HF and NH4 F are used in this part.Detectors using BOE only have closer R_0A to that using the combining method,but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE.We finally choose the combining method and fabricated the 640×512 FPA.The FPA with cutoff wavelength of 4.8 μm has the average R_0A of 6.13 × 10~9 Ω·cm~2 and the average detectivity of 4.51 × 10~9 cm·Hz~(1/2).W~(-1)at 77 K.The FPA has good uniformity with the bad dots rate of 1.21%and the noise equivalent temperature difference(NEDT) of 22.9 mK operating at 77 K.