2016年9月26日星期一

Room temperature contactless electroreflectance characterization of InGaAs/InAs/GaAs quantum dot wafers

Contactless electroreflectance (CER) mapping has been performed on InGaAs capped InAs/GaAs quantum dot (QD) wafers of 2 inch diameter grown by molecular beam epitaxy. The CER spectra have revealed several features related to InAs self-assembled QDs and a quantum well (QW) formed of the InAs wetting layer and the InGaAs cap layer. The particular optical transitions have been identified based on theoretical calculations of the energy levels in the InAs/InGaAs/GaAs wetting layer related step-like QW, performed within the effective mass approximation. The influence of possible uncertainties in cap content or band offsets has also been analysed. The advantages of modulation spectroscopy, namely its absorption-like character and high sensitivity to optical transitions with even very low oscillator strength including those between the excited states, have allowed the energies of all the transitions along the wafer to be followed. The latter has shown that within experimental error the transition energies are independent of the position of the probing spot on the sample. It demonstrates not only a very high uniformity of the dot ensemble but also the wetting layer related QW and hence also the content and thickness of the InGaAs cap.

Keywords:  Contactless electroreflectance (CER);  InGaAs;  InAs/GaAs quantum dot (QD) wafers;  InAs wetting;  InGaAs cap layer; 

Source:  iopscience

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2016年9月19日星期一

Gate-induced transition between metal-type and thermally activated transport in self-catalyzed MBE-grown InAs nanowires

Electronic transport properties of InAs nanowires are studied systematically. The nanowires are grown by molecular beam epitaxy on a SiOx-covered GaAs wafer, without using foreign catalyst particles. Room-temperature measurements revealed relatively high resistivity and low carrier concentration values, which correlate with the low background doping obtained by our growth method. Transport parameters, such as resistivity, mobility, and carrier concentration, show a relatively large spread that is attributed to variations in surface conditions. For some nanowires the conductivity has a metal-type dependence on temperature, i.e. decreasing with decreasing temperature, while other nanowires show the opposite temperature behavior, i.e. temperature-activated characteristics. An applied gate voltage in a field-effect transistor configuration can switch between the two types of behavior. The effect is explained by the presence of barriers formed by potential fluctuations.

Keywords:  InAs nanowires;  GaAs wafer;  

Source: iopscience

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2016年9月11日星期日

Mid-wavelength type II InAs/GaSb superlattice infrared focal plane arrays

Highlights

•The superlattice materials were grown with both GaAs-like and InSb-like interface to balance the strain.

•The pixel was isolated by chlorine-based plasma etching together with citric acid-based chemical wet etching.

•The first device with 50% cutoff wavelength of 4.1 μm shows NETD~18 mK from 77 K to 100 K.
•The NETD of the second device with 50% cutoff wavelength at 5.6 μm is 10 mK at 77 K.

We have demonstrated 384 × 288 pixels mid-wavelength infrared focal plane arrays (FPA) using type II InAs/GaSb superlattice (T2SL) photodetectors with pitch of 25 μm. Two p-i-n T2SL samples were grown by molecular beam epitaxy with both GaAs-like and InSb-like interface. The diode chips were realized by pixel isolation with both dry etching and wet etching method, and passivation with SiNx layer. The device one with 50% cutoff wavelength of 4.1 μm shows NETD~18 mK from 77 K to 100 K.of the other device with 50% cutoff wavelength at 5.6 μm is 10 mK at 77 K. Finally, the T2SL FPA shows high quality imaging capability at the temperature ranging from 80 K to 100 K which demonstrates the devices’ good temperature performance.

Keywords: Type II InAs/GaSb superlattice;  Focal plane arrays;  Mid-wavelength infrared

Source: Sciencedirect

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2016年9月1日星期四

P-InAsSbP/n-InAs single heterostructure back-side illuminated 8×8 photodiode array

Highlights

•BLIP regime starting from 190 K at 3 μm.
•Capacitance as small as 1.3×10-7 F·cm-2, 80 K.
•Good uniformity of diode parameters in 8×8 PD matrix.

P-InAsSbP/n-InAs/n+-InAs single heterostructure photodiode array with linear impurity distribution in the space charge region and “bulk” n-InAs absorbing layer has been fabricated by the LPE method and studied for the first time. Unlike all known InAsSbP/InAs PDs with an abrupt p-n junction the linear impurity distribution PDs potentially suggest lower compared with analogs capacitance and tunneling current. Indeed the developed photodiodes showed good perspectives for use in low temperature pyrometry as low dark current (8×10-6 A/cm2, Ubias=-0.5 V, 164 K) and background limited infrared photodetector (BLIP)  regime starting from 190 K have been demonstrated. High photodiode performance is thought to be due to above peculiarities of the impurity distribution as well as low defect density in P-InAsSbP/n-InAs/n±
-InAssingle heterostructure.

Keywords

  • HOT mid-IR detectors;
  • InAs photodiodes;
  • Infrared sensors;
  • Dark current;
  • Backside illuminated photodiodes;
  • Pyrometry;
  • IR gas sensors
Source: Sciencedirect

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