C. Besikci

Molecular beam epitaxial growth of high quality InSb

In this letter we report on the growth of high quality InSb by molecular beam epitaxy that has been optimized using reflection high energy electron diffraction. A 4.8 μm InSb layer grown on GaAs at a growth temperature of 395 °C and a III/V incorporation ratio of 1:1.2 had an x‐ray rocking curve of 158 arcsec and a Hall mobility of 92 300 cm2 V−1 at 77 K. This is the best material quality obtained for InSb nucleated directly onto GaAs reported to date.

Anomalous Hall effect in InSb layers grown by metalorganic chemical vapor deposition on GaAs substrates

InSb epitaxial layers have been grown on GaAs substrates by low‐pressure metalorganic chemical vapor deposition. A 3.15‐μm‐thick film yielded an x‐ray full width at half maximum of 171 arcsec. A Hall mobility of 76 200 cm2/V s at 240 K and a full width at half maximum of 174 arcsec have been measured for a 4.85‐μm‐thick epilayer. Measured Hall data have shown anomalous behavior. A decrease in Hall mobility with decreasing temperature has been observed and room‐temperature Hall mobility has increased with thickness. In order to explain the anomalous Hall data, and the thickness dependence of the measured parameters, the Hall coefficient and Hall mobility have been simulated using a three‐layer model including a surface layer, a bulklike layer, and an interface layer with a high density of defects. Theoretical analysis has shown that anomalous behavior can be attributed to donorlike defects caused by the large lattice mismatch and to a surface layer which dominates the transport in the material at low tempe...

Growth of In1−xTlxSb, a new infrared material, by low‐pressure metalorganic chemical vapor deposition

We report the growth of In1−xTlxSb, a new III‐V alloy for long‐wavelength infrared detector applications, by low‐pressure metalorganic chemical vapor deposition. In1−xTlxSb with good surface morphology was obtained on both GaAs and InSb substrates at a growth temperature of 455 °C. X‐ray diffraction measurements showed resolved peaks of In1−xTlxSb and InSb films. Infrared absorption spectrum of In1−xTlxSb showed a shift toward lower energies compared to InSb spectrum. Hall mobility data on In1−xTlxSb/InSb/GaAs structure showed enhanced mobility at low temperatures compared to InSb/GaAs structure.

Detailed investigation of electron transport, capture and gain in Al0.3Ga0.7As/GaAs quantum well infrared photodetectors

We present an investigation of Al0.3Ga0.7As/GaAs quantum well infrared photodetectors (QWIPs) through detailed ensemble Monte Carlo simulations. Both two-dimensional and three-dimensional electrons are simulated with realistically evaluated scattering rates. Transport of the excited electrons is accurately modelled including the reflections from well–barrier interfaces. The details incorporated into the simulator clarified some important phenomena, as well as verifying the previous predictions. Under large bias, well accumulation occurs non-uniformly, being highest near the emitter. Contrary to previous assumptions, the L valley is found to be the origin of a significant portion of the captured electrons even under typical bias voltages. Γ–L transfer, while decreasing carrier mobility, also increases capture probability and decreases the electron lifetime, having a twofold effect on device gain. The above findings explain the large difference between the gains of AlxGa1−xAs/GaAs (with x ~ 0.3) and InP/In0.53Ga0.47As (or GaAs/InxGa1−xAs) QWIPs, as well as the bias dependence of gain. The average barrier electron velocity is close to the saturated electron velocity in bulk Al0.3Ga0.7As under moderate and large bias; however, low-field mobility is significantly lower than that in bulk material. While complementing previous work, our results offer a deeper understanding of some important QWIP characteristics by resolving the details of transport and electron dynamics in the device.

Detailed analysis of carrier transport in InAs0.3Sb0.7 layers grown on GaAs substrates by metalorganic chemical‐vapor deposition

InAs0.3Sb0.7 layers with mirrorlike morphology have been grown on GaAs substrates by low‐pressure metalorganic chemical vapor deposition. A room‐temperature electron Hall mobility of 2×104 cm2/V s has been obtained for a 2‐μm‐thick layer. Low‐temperature resistivity of the layers depended on TMIn flow rate and layer thickness. Hall mobility decreased monotonically with decreasing temperature below 300 K. A 77 K conductivity profile has shown an anomalous increase in the sample conductivity with decreasing thickness except in the near vicinity of the heterointerface. In order to interpret the experimental data, the effects of different scattering mechanisms on carrier mobility have been calculated, and the influences of the lattice mismatch and surface conduction on the Hall measurements have been investigated by applying a three‐layer Hall‐effect model. Experimental and theoretical results suggest that the combined effects of the dislocations generated by the large lattice mismatch and strong surface inversion may lead to deceptive Hall measurements by reflecting typical n‐type behavior for a p‐type sample, and the measured carrier concentration may considerably be affected by the surface conduction up to near room temperature. A quantitative analysis of dislocation scattering has shown significant degradation in electron mobility for dislocation densities above 107 cm−2. The effects of dislocation scattering on hole mobility have been found to be less severe. It has also been observed that there is a critical epilayer thickness (∼1 μm) below which the surface electron mobility is limited by dislocation scattering.

High responsivity InP-InGaAs quantum-well infrared photodetectors: characteristics and focal plane array performance

We report the detailed characteristics of long-wavelength infrared InP-In/sub 0.53/Ga/sub 0.47/As quantum-well infrared photodetectors (QWIPs) and 640/spl times/512 focal plane array (FPA) grown by molecular beam epitaxy. For reliable assessment of the detector performance, characterization was performed on test detectors of the same size and structure with the FPA pixels. Al/sub 0.27/Ga/sub 0.73/As-GaAs QWIPs with similar spectral response (/spl lambda//sub p/=/spl sim/7.8 /spl mu/m) were also fabricated and characterized for comparison. InP-InGaAs QWIPs (20-period) yielded quantum efficiency-gain product as high as 0.46 under -3-V bias with a 77-K peak detectivity above 1/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W. At 70 K, the detector performance is background limited with f/2 aperture up to /spl sim/ 3-V bias where the peak responsivity (2.9 A/W) is an order of magnitude higher than that of the AlGaAs-GaAs QWIP. The results show that impact ionization in similar InP-InGaAs QWIPs does not start until the average electric-field reaches /spl sim/25 kV/cm, and the detectivity remains high under moderately large bias, which yields high responsivity due to large photoconductive gain. The InP-InGaAs QWIP FPA offers reasonably low noise equivalent temperature difference (NETD) even with very short integration times (/spl tau/).70 K NETD values of the FPA with f/1.5 optics are 36 and 64 mK under bias voltages of -0.5 V (/spl tau/=11 ms) and -2 V (/spl tau/=650 /spl mu/s), respectively. The results clearly show the potential of InP-InGaAs QWIPs for thermal imaging applications requiring high responsivity and short integration times.

Large-Format Voltage-Tunable Dual-Band Quantum-Well Infrared Photodetector Focal Plane Array for Third-Generation Thermal Imagers

We report a large-format (640 times 512) voltage- tunable quantum-well (QW) infrared photodetector focal plane array (FPA) for dual-band imaging in the mid- and long-wavelength infrared (MWIR and LWIR) bands. Voltage-tunable spectral response has been achieved through a series connection of eight-well MWIR AlGaAs-InGaAs and 16-well LWIR AlGaAs-GaAs QW stacks grown by molecular beam epitaxy on GaAs substrate. The peak responsivity wavelength of the detectors is shifted from 4.8 to 8.4 mum as the bias is increased within the limit applicable by commercial read-out integrated circuits. The FPA with MWIR and LWIR cutoff wavelengths of 5.1 and 8.9 mum provides noise equivalent temperature differences of 20 and 32 mK (f/1.5) in these bands, respectively. The results are very encouraging for the development of low-cost large-format dual-band MWIR/LWIR FPA technology.

Demonstration and Performance Assessment of Large Format InP–InGaAsP Quantum-Well Infrared Photodetector Focal Plane Array

There have been various studies showing that InP-InGaAs quantum-well infrared photodetectors (QWIPs) are potential alternatives to AlGaAs-GaAs QWIPs in the long wavelength infrared (LWIR) band, especially for applications requiring high responsivity. Being on InP substrate, this material system also offers lattice matched mid-wavelength infrared (MWIR)/LWIR dual band QWIP stack when it is used with the AlInAs-InGaAs system. It is desirable to extend the cut-off wavelength of InP based LWIR QWIPs to , which can be accomplished by replacing the QW material with InGaAsP. In this paper, we report the first InP-InGaAsP QWIP focal plane array (FPA). The 640 512 FPA displayed remarkably low noise equivalent temperature difference (NETD) with very short integration times (46 mK at 66 K with and f/1.5 optics). The results show that these QWIPs can be operated with high responsivity (1 A/W) while offering bias adjustable gain in a wide range where the detectivity is almost constant at a reasonably high level.

Lattice-matched AlInAs-InGaAs mid-wavelength infrared QWIPs : characteristics and focal plane array performance

The AlInAs/InGaAs material system is promising for mid-wavelength infrared (MWIR) and multi-band quantum well infrared photodetectors (QWIPs) as a lattice-matched alternative to the strained AlGaAs/InGaAs system. In this paper, we report a large format (640 ? 512) AlInAs/InGaAs QWIP focal plane array (FPA) with 4.9 ?m cut-off wavelength and assess the performance of this material system for MWIR QWIP applications at both pixel and large format FPA level. We also experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by changing only the quantum well (QW) width at the lattice-matched composition. The cut-off wavelength is shifted from 4.15 to 4.9 ?m when the QW width is decreased from 30 to 23 ?, in which case a very broad spectral response (??/?p = 32%) with a reasonably high peak detectivity (5.5 ? 1010 cm Hz1/2 W?1, f/1.5) is achievable. The AlInAs/InGaAs QWIP FPA yielded excellent sensitivity with a noise equivalent temperature difference as low as 22 mK and a background limited performance (BLIP) temperature as high as 115 K with f/1.5 aperture and 300 K background. The results clearly demonstrate the potential of this material system for completely lattice-matched dual- or multi-band QWIP FPAs for third-generation thermal imagers.

Electron transport properties of Ga/sub 0.51/In/sub 0.49/P for device applications

We present Monte Carlo calculations of steady-state and transient electron transport properties of Ga/sub 0.51/In/sub 0.49/P. We have made a simulation-based comparison between Ga/sub 0.51/In/sub 0.49/P and Al/sub x/Ga/sub 1-x/As(x=0.2, 0.3). Our Monte Carlo data show that transport properties of G/sub 0.51/In/sub 0.49/P are favorable, and when the other advantages of the GaInP/GaAs system are also taken into account, this material is a good choice to replace Al/sub x/Ga/sub 1-x/As(x/spl ges/0.3). We have also calculated electron drift and Hall mobilities in Ga/sub 0.51/In/sub 0.49/P as a function of impurity concentration and temperature, and determined the effects of different scattering mechanisms on the low-field mobility. Calculated results are in good agreement with the measurements on metal organic chemical vapor deposition (MOCVD) grown samples with Hall mobilities within a factor of 0.5 of the calculated theoretical limit. It has also been found that alloy scattering is an important mobility degrading mechanism in lightly doped material at low temperatures. >