Device results from Photin wafers

In 2024 our facility receive major upgrade with installation of Hydrogen purifier based on Palladium Diffusion Membrane technology, which allow to obtain ultimate purity of hydrogen for growth of semiconductors.
The performance of grown materials were tested on InAs on SI GaAs substrates (to be reported soon) for wafer level characterization, and InAs-InAsSbP structures for device results.
We arranged quick processing and measured a couple of 200, 300, 400 and 500um diameter photodiodes from InAs/InAsSbP structure to assess its performance.

Fig. 1. InAs-InAsSbP I-V and Responsivity.
Fig. 1. InAs-InAsSbP I-V and Responsivity for various mesa diameters.

Small responsivity is justified, as this detector was illuminated through InAs n-type substrate. Though, why dark current is so small? Initially we thought that area normalization is wrong, or someone added somewhere 100x factor by accident. The dark current looked too small, and R0A too high..??
The 200-300 mesa size shows clearly larger dark currents due to sidewall leakage currents. This highlight practical importance of research on IR detector passivation, that is subject of our InnoGlobo2 project with Military University of Technology.
Currently more samples from this wafer are being processed, to measure it’s performance in illumination from top.

R0A as figure of merit of IR detectors

R0A product is a popular photon IR detector figure of merit. It is defined as the product of dynamic resistance at zero bias, R0A, by sensitive area, A. R0A is inversely proportional to the saturation current density Js of a photodiode:

R0A = kT / ( eJs)

It is possible to have high R0A, and low dark current, when the vallence barrier impede minority carrier transport and hence photocurrent, but this structure have reasonable responsivity @10mV despite being illuminated through InAs substrate. Additionally, for InAs-InAsSbP bandgap offsets are such, that they usually not form valence barrier, in opposite to InAs-AlAsSb or InAs-AlGaAsSb usually grown in MBE.

Investigation about InAs-based detectors performance

Hamamatsu, VIGO, Laser Components, Judson are the companies that offer InAs detectors, and their datasheets are first quick benchmark of what performance to expect.

Vendor Diam., um R0Atyp, Ohm.cm2 Rsh-min Ohm Rsh-typ. Ohm Jsat, A/cm2 Datasheet
VIGO 1000 0.51 50 65 0.051 PVA-3-1x1
Hamamatsu 1000 0.55 40 70 0.047 P10090-01
Judson 250 0.15 200 300 0.180 J12-18C-R250U
Judson 1000 0.20 15 25 0.130 J12-18C-R01M
Photin 500 2.10 NA 1070 0.012 Ph-IA3.5-0.5-RT
LaserComp. 500 1.37 450 700 0.019 IA35

The R0A is in range of 0.2-0.55 Ohm.cm2, except for Laser Components 1.37 Ohm.cm2.
Without doubt our results of 2.1 Ohm.cm2 clearly stand out.

Literature research at first sight shows a few publications, where InAs detectors were developed with parameters comparable to commercial :

Deeper search finally shown, that state of the art InAs detectors actually reach R0A ~2.0 Ohm.cm2, or equivalent 1e-2 A/cm2 dark current density, and it is not MBE InAs-AlAsSb, but InAs-InAsSbP materials:

Why it matters

III-V semiconductors are used for laser, detectors, modulators, SLEDs, and Photonics Integrated Circuits. GaAs lattice matched compounds are used for near infrared <1um, InP-based platform is used for 1um-~1.7um range. InAs and GaSb based platform are used for SWIR, MWIR and LWIR devices above 2um.
Looking at more mature InP-platform, we have 2 competing compounds, AlInGaAs and InGaAsP. InGaAsP devices have poorer performance than AlInGaAs, but lack of reliability risks without Alluminum, makes still InGaAsP very popular compound for InP devices and PICs.
In InP-platform MBE technology use is limited for devices and PICs, where multiple growths are required on single wafer, as MBE growth is not conformal. Hence, majority of InP devices are grown by MOCVD, it is technology of choice on market.

Type 2 superlattices InAs-InAsSb (T2SLs) are currently replacing HgCdTe infrared detectors in commercial market of SWIR/MWIR/LWIR devices.
MBE technology in SWIR/MWIR/LWIR use InAs/GaSb or InAs/InAsSb T2SLs with AlSb/AlAsSb/AlGaAsSb barriers. The Al-based barriers give reliability risks in similar way to AlInGaAs in InP platform.
This is why we expect, that in longer term MOCVD InAs/InAsSbP will be favoured for SWIR/MWIR/LWIR IR detectors and PICs applications.

Key take away

No other Polish company, institute or university was able so far to showcase InAs ~3.5um detectors based on III-Sb semiconductors with better dark current performance than our reported results.
Currently Photin ability to grow Sb-based, 6.1A family of III-V compounds in MOCVD provide researchers unique opportunities in SWIR/MWIR device development.