Substrates Used in Photodectors

university wafer substrates

Substrates to Fabricate Photodetectors for the near IR Spectrum

An electrical engineer requested the following quote:

I am an electrical engineering student working on a senior thesis.  I am working on developing a process for my research group to fabricate photodetectors for the near IR spectrum on a wafer which can be used to fabricate conventional electrical devices as well.

I was wondering, do you have any wafers in stock with germanium deposited on silicon?  If not, is there some way that you can fabricate such a wafer for me?  Currently, we do not have the capability to do deposit germanium on silicon in our own facilities.

Reference #93774 for specs and pricing.

Get Your Quote FAST!

Satellite/Space Sun Sensor Development

A electronics engineer requested the following quote:

We have now more clarity on the characteristics of  the wafer we are looking for. The details are as given below. If you have wafers closely meeting these requirements please let us know the cost and delivery details. We will then be able proceed further.

Application Description: 4 Quadrant Segment Position Sensitive Detector (PSD)

Photodetector Electro-Optical Specification Per Element:

  • Die Size: 25mm x 25mm
  • Active Area Size: 20mm x 20mm
  • Operating Wavelength: 200nm ~ 1100nm
  • Applied Bias: negative
  • Max. Dark Current @ ~ < 3nA
  • Max. Capacitance @ ~ < 3000pF

 Mechanical / Packaging Specifications:

  • Isolated Chip: Yes
  • Common Anode or Cathode: Common Anode
  • Chip Only: with Solderable Pads

Environmental Requirements:

  • Space Environment: Low Earth Orbit
  • Temperature: -40°C ~ 75°C

Reference #94426 for specs and pricing.

GaN and AlGaN Photodetectors

A MEMS researcher requested a quote for the following:

I need GaN and AlGaN, small wafers or pieces, but probably needs to be single crystal since we are making small electronic devices (photodetectors) that must have low leakage current. I will also consider SiC but need to think about it.

f you have special wafers made for someone else, that have already been prepared for LED or semiconductor devices (doped layers or multiple layers) that would be great. 

We can piggy-back.  Looking for a quick way to make diodes on high band-gap matetrial for blue/UV.

Reference #115249 for specs and pricing.

Black Silicon for Photodetector Applications

Black silicon is a semiconductor material, a surface modification of silicon with very low reflectivity and correspondingly high absorption of visible (and infrared) light. The modification was discovered in the 1980s as an unwanted side effect of reactive ion etching (RIE). Another method for forming a similar structure was developed at Harvard University (1998).

Black silicon is a needle-shaped surface structure where needles are made of single-crystalline silicon and have a height above 10 microns and diameter <1 micron. Its main feature is an increased absorption of incident light – the high reflectivity of the silicon, which is usually 20–30% for quasi-normal incidence, is reduced to about 5%. This is due to the formation of a so-called effective medium by the needles. Within this medium, there is no sharp interface, but a continuous change of the refractive index that reduces Fresnel reflection.

The unusual optical characteristics, combined with the semiconducting properties of silicon make this material interesting for sensor applications. The potential applications include:

  • Image sensors with increased sensitivity
  • Thermal imaging cameras
  • Photodetector with high efficiency through increased absorption
  • Mechanical contacts and interfaces
  • Terahertz applications
  • Solar Cells

Undoped Silicon Wafers Used to Fabricate PIN-Type Photodetector Array

A materials science engineer requested the following quote:

We are always looking for 500 - 600um thick DSP <100>  3" >8K FZ Si wafers. If you have in hand please let us know.

We will use this wafers for PIN type photodetector array. Do you have any wafer recommendation for this purpose?

UniversityWafer, Inc. Quoted:
Item   Qty.   Description
BN99. 10/25/50  

  • Silicon wafers, per SEMI Prime, P/P 3"Ø×525±25µm
  • FZ Intrinsic undoped Si:-[100]±0.5°
  • Ro > 8,000 Ohmcm
  • Both-sides-polished
  • SEMI Flats (two)

Reference #131421 for more specs and pricing.

What Substrates Are Used in Photodetectors?

A photodiode is a semiconductor device that generates a current based on a signal of light. It can be used for analog measurement and for control, switching, and digital signal processing.

The critical performance parameters of a photodiode include spectral responsivity, dark current, response time, and noise-equivalent power. These parameters are important for optical communication applications.

Transparent Metal Electrodes

There is a growing need for transparent electrodes to facilitate the development of flexible photodetectors. Transparent metal electrodes, such as Indium Tin Oxide (ITO) and copper-doped tin oxide (CTO), are widely used to create photodetectors with high responsivity and low dark current. They can be deposited by sputtering and annealed after deposition, and they offer an excellent opportunity to combine light transmission with high electrical conductivity.

In addition, these materials can also be fabricated by various lithographic processes, such as inkjet printing. The most popular method of preparing these electrodes is through top-down techniques, where a thin film of metal is etched onto a substrate. Other methods include bottom-up approaches, where the thin film is patterned using a stamp.

The use of these conductive electrodes has been a major focus of researchers in recent years, especially as the need for flexible electronic devices grows. Although these electrodes do not meet all the needs of modern flexible devices, their performance can be improved by combining different elements or novel structures.

One potential alternative is a dielectric-metal-dielectric (DMD)-based electrode. These electrodes consist of a thin metallic film sandwiched between two antireflection dielectrics to induce high transparency. Some studies have shown that a variety of conductive films can be used to prepare these electrodes, including graphene, carbon nanotubes, and Ga2O3 nanostructures.

These studies show that these structures can be prepared by room-temperature deposition and that they can achieve excellent light transmittance and good bending stability, even when the metal layer is only 6 nm thick. However, some of these studies do not have a clear description of the changes in sheet resistance of these structures, so further research on their performance is needed.

Another option for creating a flexible electrode is to use a nanoimprinted metal film on a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)-coated substrate, as shown in Figure 1. In this structure, the Cu electrode is transferred to the PEDOT:PSS-coated glass substrate via a flexible PDMS stamp.

The nanoimprinted Cu electrode exhibited a high average absolute transmittance of 88.4% over the visible range and a high sheet resistance of 18.6 O sq-1, as shown in Figure 2. This electrode was fabricated by physical-vapor-deposition (PVD) on a PET substrate and shows that the relative transmittance can be improved by integrating an ultrathin Cu-doped Ag film into an optimized DMD structure.

Metal Back Contacts

What substrates are used in photodetectors is a critical issue that must be addressed to achieve the best possible performance. One popular approach is to use transparent metallic electrodes, such as ITO or CTO, which have a high resistance that limits bandwidth and thermal noise. These electrodes can be easily deposited by sputtering and can also be annealed to increase the electrical performance.

Transparent metal electrodes are useful for a variety of applications, including optical communication and remote sensing. However, they typically exhibit higher resistivity than Si and must be annealed after deposition to improve their electrical performance.

An alternative approach to reducing dark current in metal-semiconductor-metal (MSM) photodetectors is to assemble interdigitated metal-insulator-semiconductor-insulator-metal (MISIM) devices on thin oxide/Si substrates [45,52]. The presence of an insulator layer effectively reduces the dark current by a factor of 5.2 and reduces the resistance of the device by a factor of 20.

The MISIM devices fabricated in this study had a spectral responsivity of 905.5 A/W, and were able to achieve an excellent photocurrent-to-dark current ratio over 104 with high switching ratio and fast response. This is an important property for future NIR-MIR optoelectronic applications.

In contrast, MSM detectors have a characteristic defect that negatively affects their responsivity: the electrodes actually “shadow” the active area and absorb or reflect incident light that is needed to trigger a response. This is an inherent weakness of the MSM structure that has limited its acceptance in the commercial arena and prevented further development of this technology.

Nevertheless, efforts have been made to overcome this problem. One of these approaches is to use unequal work function Schottky contacts in combination with dissimilar doping to reduce the asymmetry caused by the applied bias. This approach is commonly employed in organic photovoltaics, where it can be incorporated into the semiconductor without the need for a separate doping solution.

Other strategies for reducing the dark current in MSM devices include increasing the barrier height of the Schottky contact. In some instances, cryogenic processing can be used to alter the barrier height. This is often a more effective way of improving MSM devices as the effect is gradual and can be controlled.

Ohmic Contacts

Ohmic contacts are an important component of many semiconductor devices. This includes p-i-n photodiodes, photoconductors, Schottky diode detectors, and advanced photodetectors (APDs).

For these devices, ohmic contacts are required to minimize the negative effects of parasitic resistance on device performance. Parasitic resistance can arise from a number of factors, including oxidation, annealing, and surface roughness. It can also affect the ability to detect and process signals.

In general, the ohmic contact consists of an alloyed or sintered metal layer that is formed between the substrate and a highly doped semiconductor. Most often, this metallization is gold with a dopant such as n- or p-type germanium, beryllium, or zinc, although nickel may also be used.

The metallization is usually obtained by evaporation of the aqueous solution, and then the surface of the resulting alloyed layer is thermally annealed to form a smooth, well-defined contact structure. A variety of ohmic contact metallizations have been developed for a wide range of semiconductors, but they can exhibit various limitations.

One of the main challenges is to fabricate ohmic contacts that exhibit high uniformity across the entire contact area, especially on crystalline regions. This is particularly a concern for III-V materials such as gallium arsenide and indium phosphide, where the underlying structure is not pristine.

Another challenge is to ensure that the ohmic contact is stable over the lifetime of the device. This requires that the intermetallic reaction is limited during contact processing, and that there are no excessive stresses in the metal films, the underlying dielectric patterning layer, and the underlying semiconductor.

Finally, a critical factor for the success of an ohmic contact is the ability to realize a low barrier height at the metal/semiconductor interface. This is known as the Schottky barrier height (SBH). The SBH at a metal-semiconductor contact is intimately connected to the contact resistance, and reducing the SBH is an important step towards energy-efficient and high-speed semiconductor devices.

As a result, the fabrication of ohmic contacts has been a major research challenge for a wide variety of semiconductors. This includes both silicon and compound semiconductors such as GaAs and AlGaAs.

Silicon Substrates

Silicon is the most widely used semiconductor material in the world. It is the key component of RAM chips and other electronic devices, making it important in boosting the digital era.

There are two types of substrates that are commonly used in photodetectors: silicon wafers and silicon nitride wafers. Silicon wafers are ultra-flat disks that have very small irregularities and reflect the most light. They are manufactured by a variety of methods, including the vertical bridgeman method and the Czochralski pulling method.

They are available in several sizes, but the smallest is a 0.5" diameter. They are primarily used as thin film research, sample substrates, or micro-fabrication substrates, and can also be diced into smaller pieces using a scriber. The diced pieces are shipped in a wafer carrier for easy handling.

Inseto offers a range of high-quality, pristine, uncut and untreated, bare and wafer-diced silicon, glass and compound semiconductor wafers to university, research and industrial sectors. They are ideal for thin film and semiconductor research, and can be pre-processed with oxide and nitride coatings, grid patterns or custom processing.

One of the most interesting applications for a silicon-based photodetector is in the near-infrared (NIR) region. NIR detectors have been developed for a number of applications, such as fibre optic telecommunication, quality control and imaging systems. However, they have not been fully exploited as monolithic integration of the optoelectronic building blocks into the silicon-based CMOS process is difficult because of the crystal lattice mismatch between the material systems.

To overcome this challenge, we have incorporated a heterojunction of silica nano-islands and Ge nanoclusters on silicon-on-insulator (SOI) substrates using hot-wall epitaxy. This heterojunction has a very low band gap and can be used for NIR detectors in silicon-based CMOS.

The resulting device has a low-voltage, high-quality photodetector that is capable of detecting UV and visible light. The peak EQE of this device is 1.03 A/W, which is comparable to anatase TiO2-based devices.

The Ge clusters are deposited on the Si islands by chemical vapour deposition. The resulting nano-islands are then polished by a RF polishing machine. The resulting crystals have a tensile strain of up to 0.5%, which can be measured by grazing-incidence diffraction.

What is a Photodetector Array?

A semiconductor substrates such as silicon or Si are used to fabricate photodiodes, which are then disposed of in an array. A common electrode is used to connect the individual detectors and enable measurements. Photodiode arrays can be used in research equipment and various intensity imaging applications. Silicon photodiodes are the most common type of detector arrays. They are susceptible to visible and near-infrared light, which is ideal for light sensors or camera systems. Show Source Texts
A photodiode array spectrophotometer is a device that uses a diode array spectrophotometer to allow for long wavelength photodiode arrays that make the fast spectral acquisition possible. The photodiodes are arranged in many wavelengths and can be used as an angle sensor or a simple, balanced detector. Photodetector arrays can have thousands of detectors, making them ideal for position sensors and allowing for precise position measurements. Photodetector arrays are also used in one-dimensional arrays to measure fast chemical reactions. Two diodes can be used together to study the kinetics of response and obtain valuable data. Show Source Texts
Photodetector arrays provide an excellent tool for analyzing light data, as it comprises multiple-element photodiodes that can be arranged in any configuration. This allows for more efficient methods of measuring the intensity and wavelength of light. AMS technologies supply tetra lateral detectors that measure the light intensity from a single diode in four directions, providing an efficient method for studying two-dimensional image planes.