Demonstration of HOT photoresponse of MWIR T2SLs InAs/InAsSb photoresistors

BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES, Vol. 67, No. 1, 2019 DOI: 10.24425/bpas.2019.127343 Demonstration of HOT photoresponse of MWIR T2SLs InAs/InAsSb photoresistors K. MICHALCZEWSKI 1*, T. Y. TSAI 2, P. MARTYNIUK 1, and C.H. WU 2 1 2 Institute of Applied Physics, Military University of Technology, 2 Urbanowicza Str., 00-908 Warsaw, Poland Graduate Institute of Photonics and Optoeletronics, National Taiwan University, Roosevelt Str., 10617 Taipei, Taiwan Abstract. We report on the photoresponse of mid-wavelength infrared radiation (MWIR) type-II superlattices (T2SLs) InAs/InAsSb high operating temperature (HOT) photoresistor grown on GaAs substrate. The device consists of a 200 periods of active layer grown on GaSb buffer layer. The photoresistor reached a 50% cut-off wavelength of 5 µm and 6 µm at 200 K and 300 K respectively. The time constant of 30 ns is observed at 200 K under 1 V bias. This is the first observation of the photoresponse in MWIR T2SLs InAs/InAsSb above 200 K.. Key words: HOT, MWIR T2SLs InAs/InAsSb, photoresistor. 1. Introduction From the physics point of view type-II superlattices (T2SLs) are interesting material. The fundamental lower Auger recombination [1], stronger bonds and structural stability [2], lower bandto-band tunnelling due to larger electron effective mass [3], as well as growth and processing technology [4] make T2SLs a potential candidate to replace expensive HgCdTe and to operate at higher temperatures. T2SLs InAs/ InAs1 ¡ x Sbx and InAs/ GaSb concept have been widely studied over last 2 decades. Due to the fact that minority carrier lifetime in InAs/ GaSb T2SLs is limited by Shockley-Read-Hall (SRH) mechanism, the InAs/ InAs1 ¡ x Sbx T2SLs material is considered as alternative for infrared laser and detector application. The absence of Gallium (Ga) being responsible for above mentioned recombination centers allows T2SLs InAs/InAsSb to have much longer lifetimes, up to 10 µs for undoped material in mid-wavelength infrared radiation (MWIR) region [5]. GaSb substrate is the best choice to grow T2SLs on due to its lattice constant being between InAs and InAsSb [6]. From the other point of view in order to produce cheap infrared focal plane arrays (IR FPAs) it is recommended to utilize GaAs substrate. GaAs has better structural, optical and thermal properties than GaSb. In addition, these substrates are more affordable and available as large size “epi-ready” wafers up to 6 inch in diameter. Transparent GaAs substrate allows for the backsided device illumination and fabrication of monolithic optical immersion [7]. The interfacial misfit array (IMF) is the best technique which allows to reach a high quality GaSb buffer layer on GaAs substrate. In IMF the mismatch between GaSb and GaAs is accommodated at the interface by formed a 2D periodic array of 90° dislocation (Lomer dislocation) along both [110] and *e-mail: Manuscript submitted 2018-01-29, revised 2018-05-21, initially accepted for publication 2018-08-04, published in February 2019. Bull. Pol. Ac.: Tech. 67(1) 2019 [1‒10] direction [8]. In this paper, InAs/InAsSb T2SLs grown by molecular beam epitaxy (MBE) is studied. High-resolution X-ray diffraction (HRXRD), optical characterizations made of photoluminescence (PL), spectral response and response time measurements performed on InAs/InAsSb T2SLs are reported and analyzed. 2. Growth description The T2SLs InAs/InAsSb layers were grown by a RIBER Compact 21-DZ solid source MBE system, on GaAs (001) substrates. The system is equipped with double filament effusion cells for Ga and In, and with valved cracker cells for As and Sb. As2 and Sb have been used. The manipulator thermocouple was used to monitor the substrate temperature. Growth temperature was calibrated from the GaAs substrate deoxidization temperature. After the deoxidation of the GaAs substrate at 675°C under As2 overpressure, a 250 nm-thick GaAs layer was first deposited at 655°C to smooth the substrate surface. The reflection high-energy electron diffraction (RHEED) surface reconstruction showed a 2£4 pattern characteristic for a As-rich surface. Afterwards in order to reach Ga rich surface the Ga shutter was closed to let the As adatoms desorb. When the 4£2 GaAs surface reconstruction was generated the substrate temperature was reduced to 505°C under Sb overpressure. The reconstruction of the surface transformed to a 2£8 revealing that the Sb adatoms have combined with Ga rich surface. After stabilization of the temperature at 505°C the Ga shutter was opened and the GaSb layer growth started. Instantaneously the spotty RHEED pattern appeared at the growth of the first few monolayers indicating a 3D growth mode. Subsequently after next few monolayers the 1£3 surface reconstruction was generated indicating a 2D growth mode. The thickness of GaSb buffer layer was set to be » 1.0 µm. The growth rate for the GaSb layer was 0.76 µm/h while the BEP (beam equivalent pressure) group V/III flux ratio (Sb/Ga) was set to be 5. Then the substrate was cooled down 141 K. Michalczewski, T.Y. Tsai, P. Martyniuk, and C.H. Wu to 425°C under Sb overpressure. When the temperature was stabilized the T2SLs growth started. During the growth short soaking of As and As + Sb time was used to minimize surface composition changing at the interfaces. The growth rate of InAs layer was set to 0.5 ML/s and InAsSb » 0.53 ML/s. Prior to the growth the calibration processes were performed to reach required composition of InAsSb layer. Strain calculation was evaluated by equation from work by Polly et al. [9]. alytical software. The full-width at half-maximum (FWHM) of the zeroth-order peak (2Θ-ω) is equal to 147 arcsec. In Fig. 1a, the 2Θ-ω scan shows two diffraction peaks, at the position 2Θ = 66.07° and 2Θ = 60.73°, corresponding to GaAs substrate and GaSb buffer layer, respectively. The strain balance has not been reached for that sample. The sample is in tensile mismatch in the growth direction. Figure 1b presents the architecture of T2SLs InAs/InAsSb. 3. High-resolution X-ray diffraction (HRXRD) 4. Photoluminescence (PL) measurements X-ray diffractometer of PANalytical X’Pert was utilized to assess the structural properties of the InAs/InAsSb T2SLs. The Cu Kα1 radiation (λ = 1.5406 Å) originating from a line focus was used. The X-ray beam was monochromatized by four bounce, Ge (004) hybrid monochromator. The measurements were performed in 2Θ-ω direction. Figure 1a represents the high-resolution X-ray diffraction pattern around the symmetric 004 reflection of 200 periods with simulation made by PAN- The PL emission was analyzed using a Bruker Vertex v70 Fourier transform infrared (FTIR) spectrometer. The sample was placed in a closed cryostat, that allows a precise control of the temperature from 40 K to 300 K. 630 nm diode with mechanical chopper was used to the sample excitation the sample through a CaF2 window. The whole optical path was under vacuum cond (...truncated)