Youichi Nagai

MOVPE grown InGaAs/GaAsSb type II quantum well photodiode for SWIR focal plane array

Infrared sensors with type II quantum well structure have gained great attention and have shown advanced progress. InGaAs/GaAsSb type II quantum well structures are considered as an attractive material system for realizing low dark current PDs owing to lattice-matching to InP substrate. In this report, we describe successful operation of PIN-PDs with InGaAs/GaAsSb quantum wells grown by metal-organic vapor phase epitaxy (MOVPE). MOVPE method is well-known to have good uniformity which leads to mass-production of focal plane array. Planer type pin-PDs were adopted. The p-n junction was formed in the absorption layer by the selective diffusion of zinc. Electrical and optical characteristics of pin-PDs such as well number dependence of responsivity, were investigated. Dark current was 9.0 μA/cm2 at 233 K, which has better uniformity compared to those of MBE sample, and responsivity of 0.8 A/W in SWIR region were obtained. This result indicates that planer photodiode using MOVPE grown InGaAs/GaAsSb type II quantum wells is a promising candidate for consumer applications.

Low dark current SWIR photodiode with InGaAs/GaAsSb Type II quantum wells grown on InP substrate

For sensing short wavelength infrared (SWIR) region (1.0–2.5 µm), photodiodes with In<inf>0.53</inf>Ga<inf>0.47</inf>As/GaAs<inf>0.5</inf>Sb<inf>0.5</inf> type II quantum well structure grown on InP substrate by solid source molecular beam epitaxy (MBE), were successfully fabricated. Low dark current was obtained by improving GaAsSb crystalline quality.

Uncooled SWIR InGaAs/GaAsSb type-II quantum well focal plane array

Low dark current photodiodes (PDs) in the short wavelength infrared (SWIR) upto 2.5μm region, are expected for many applications. HgCdTe (MCT) is predominantly used for infrared imaging applications. However, because of high dark current, MCT device requires a refrigerator such as stirling cooler, which increases power consumption, size and cost of the sensing system. Recently, InGaAs/GaAsSb type II quantum well structures were considered as attractive material system for realizing low dark current PDs owing to lattice-matching to InP substrate. Planar type PIN-PDs were successfully fabricated. The absorption layer with 250 pair-InGaAs(5nm)/GaAsSb(5nm) quantum well structures was grown on S-doped (100) InP substrates by solid source molecular beam epitaxy method. InP and InGaAs were used for cap layer and buffer layer, respectively. The p-n junctions were formed in the absorption layer by the selective diffusion of zinc. Diameter of light-receiving region was 140μm. Low dark current was obtained by improving GaAsSb crystalline quality. Dark current density was 0.92mA/cm2 which was smaller than that of a conventional MCT. Based on the same process as the discrete device, a 320x256 planar type focal plane array was also fabricated. Each PD has 15μm diameter and 30μm pitch and it was bonded to read-out IC by using indium bump flip chip process. Finally, we have successfully demonstrated the 320 x256 SWIR image at room temperature. This result means that planer type PD array with the type II InGaAs/GaAsSb quantum well structure is a promising candidate for uncooled applications.

MBE Growth of Thick InGaAsN Layers Lattice-Matched to InP Substrates

We investigated the effects of growth temperature and As/III flux ratio on thick InGaAsN layers lattice-matched to InP substrates. We found that surface morphology and crystalline quality can be improved by growing at temperature higher than 480degC. By optimizing the As/III flux ratio, we successfully obtained the InGaAsN layer with PL wavelength as long as 2.03 mum at room temperature.

MBE Growth of Thick InGaAsN Layers with Absorption Edge at 1.95?m on InP Substrates

Thick InGaAsN layers were successfully grown on InP substrates by molecular beam epitaxy (MBE) method. The secondary ion mass spectroscopy (SIMS) analysis showed the nitrogen concentration in an InGaAsN layer was uniform. X-ray diffraction (XRD) measurements showed the crystalline quality of InGaAsN layer can be improved by post-growth annealing at a proper temperature. XRD and photoluminescence (PL) measurements showed that using As2 instead of As4 as arsenic source during growth also improved the crystalline quality of InGaAsN layer