Undoped Silicon Wafers: Intrinsic and Float Zone Substrates

Undoped Silicon Wafer Applications: Optics, RF, and Thin Films

Undoped silicon wafers are wafers made from pure silicon that have not been intentionally doped with impurities. Doping is the process of introducing impurities, such as phosphorus or boron, into the crystal structure of a semiconductor material in order to alter its electrical properties.

High-resistivity undoped silicon is used in optical experiments, substrate characterization, and selected RF and millimeter-wave devices. It remains a semiconductor: its conductivity depends on temperature, illumination, and residual electrically active impurities. Select the high-resistivity silicon substrate to match the electrical and optical conditions of the experiment.

Undoped wafers can serve as substrates for thin-film coatings, MEMS research, and optical measurements. If a process requires a dielectric layer, specify the thermal silicon dioxide coating separately, including oxide thickness and which wafer surfaces should be coated.

For beam-combining and infrared experiments, confirm the operating wavelength, wafer thickness, surface finish, and acceptable optical losses. Double-side polished undoped wafers are commonly requested when the beam passes through both surfaces. The researcher examples below show how substrate requirements change with the experiment.

High-Resistivity Undoped Silicon for Millimeter-Wave Switching

A corporate scientist has used the following high-resistivity silicon wafer to form the main switching mechanism of the light-activated millimeter-wave switch.

Si Item #3225
150mm Undoped <100> >10,000 ohm-cm 675um DSP Prime

Float Zone Silicon Characterization: FTIR and Material Testing

Client asks: We are looking for service to check quality of our Float Zone (FZ) silicon

We can prepare samples in rod form, for example diam. x length :12x (20-40)mm.
We have plan check 30 samples at low temperature (B ; Ph; Sb; Al; As may be you have more possibilities?)And ~30-40 samples of poly and mono silicon at room temperature (O2 & C)We have plan delivery not less 3 pieces for each type of measurements in one delivery give me quotation for such service please.

Answer:

We can certainly measure Carbon and Oxygen content of your FZ Silicon rod samples. We normally use a wafer 3mm thick, but we can slice it from your rods. We can do that for polycrystalline and monocrystalline silicon.

We can measure crystallographic orientation and Etch-Pit-Density of your material.
We can also measure type and resistivity of your material, up into 20,000 Ohmcm range. These are significant quality measurements

I do not understand what you mean by "We have plan check 30 samples at low temperature (B ; Ph; Sb; Al; As may be you have more possibilities?)".
Is your FZ Silicon ultra high purity (hence ultra high resistivity) and you want chemical analysis of residual impurities (B, Ph, Sb, As, Al) or do you chemically dope your FZ silicon with these elements and you want to measure the concentration of these elements and resultant resistivity?

To test the quality of your FZ silicon you also should measure Minority Charge Carrier Lifetime and Dominant Charge Carrier Mobility.

Client Replies

Currently now, I interesting in control of Carbon & Oxygen content in samples, which you make from our small rods.
Give me commercial offer for such measurements, please
About concentration of some impurities in FZ siliconAt the low temperature , like temperature clouse to lequid He, possible to check concentration of impurities which I indicated at ppta level. When I ask you about other possibilities, I mean, may be you have methods how check in same conditions (He Temperature) another impurities. We are working with different feedstocks and we looking for such possibilities worldwide.

Plant Response:

I think that now I understand this situation.

FTIR is the best measurement for determining minute quantities Carbon and Oxygen in Silicon.
FTIR measurement at room temperature is adequate to monitor Oxygen in CZ crystallized Silicon.
However, to achieve the sensitivity required to meaningfully measure Oxygen and Carbon in FZ crystallized Silicon, where they are present in much smaller quantities, one needs to do the FTIR measurement at the temperature of liquid Helium.

We have the equipment to do FTIR at liquid Helium temperature, but we have not used it under cryogenic conditions for some time and we would have to purchase a supply of liquid Helium. Also, it is uneconomical to measure one sample at a time. We need to measure a series of samples, while the liquid Helium lasts, for once it boils away, we need to purchase a new bottle.

Given above limitations, if you do want to pursue the matter, we would be happy to cooperate.

Wafer Specs Provided to Client

Item Qty. Description
GL22. 1/5/25 Measure by FTIR according to SEMI standards, Carbon and Oxygen content
of FZ Intrinsic undoped Silicon ingots, 12mmØ × (20-40)mm, NO Flats.

Note: The quote is for analysis of 1 or 5 or 25 staples sent together as one package.

Here is another researcher and what he uses undoped silicon wafers for:

"We use the wafer as a beam combiner to get a visible and infrared beam colinear in a nonlinear optical setup. For this, cleaving right angles is very helpful. Polished on both sides is essential as is undoped."

Double-Side Polished Undoped Silicon for Beam Combiners

Undoped Si Item #3193
100mm Undoped (100) >10,000 ohm-cm 525um DSP Prime

Typical Researcher Request:

"We need Undoped Silicon Wafers with Oxide layer should have a layer of 1 micron. In addition we are going to use them mainly for optical measurements, hence the impurity levels should not be too high."

Client with our help chose the following wafers:

Undoped Silicon Wafers with Thermal Oxide Layers

Item 3225 - 150mm Undoped (100) 650um SSP Test 1um Oxide Silicon Wafer

What Are Undoped and Intrinsic Silicon Wafers?

Undoped silicon is manufactured without intentionally adding electrically active dopants. In wafer catalogs it is often described as intrinsic silicon. In semiconductor physics, intrinsic behavior refers to charge carriers generated by the material itself rather than by dopants. Real wafers can still contain residual impurities and crystal defects, so the label alone does not specify absolute purity, carrier lifetime, or resistivity.

Undoped Silicon vs. P-Type and N-Type Silicon

Doped silicon contains intentionally introduced dopants that control its electrical properties. Boron commonly produces p-type silicon, while phosphorus, arsenic, or antimony can produce n-type silicon. Both lightly and heavily doped wafers exist; conductivity type does not require a high dopant concentration. Choose between undoped and doped silicon according to the device design and required resistivity.

Why Choose Float Zone Silicon for High-Purity Research?

Float Zone (FZ) silicon is grown without a quartz crucible, which helps reduce oxygen incorporation compared with Czochralski (CZ) silicon. This makes FZ material useful for experiments requiring low oxygen content and high resistivity. FZ describes a crystal-growth method, while undoped describes intentional doping: Float Zone silicon can also be intentionally doped.

How Is Undoped Silicon Wafer Resistivity Specified?

Silicon wafer resistivity is expressed in ohm-centimeters (Ω·cm) and should be specified as a measured range or lower limit. The research examples and wafer table on this page include values above 2,000, 5,000, 10,000, and 20,000 Ω·cm. These are item-specific specifications, rather than a single definition of undoped silicon. Confirm the measurement conditions, uniformity, and any required test report for the selected lot.

Choosing Diameter, Thickness, Orientation, and Surface Finish

Match the wafer diameter and substrate thickness to your holder, processing equipment, and experiment. Specify crystal orientation, thickness tolerance, total thickness variation (TTV), and bow/warp limits where relevant. Select single-side polished (SSP) silicon when one polished face is sufficient, or double-side polished (DSP) silicon when both faces require a polished finish. State any surface roughness or flatness acceptance criteria explicitly.

For smaller samples, request diced silicon substrates with the finished dimensions and edge-quality requirements. For oxide-coated substrates, include thermal oxide specifications, coating thickness, and whether one or both sides should be coated. Wafer price depends on the complete specification, processing steps, grade, and quantity.

Request Undoped Silicon Wafers for Your Experiment

Send your required diameter, thickness, orientation, resistivity, surface finish, quantity, and intended use. Note whether FZ growth, low oxygen content, optical polishing, or material characterization is required. Browse undoped and intrinsic silicon wafers online or use the quote form to discuss a custom substrate specification.

Technical references: IUPAC definition of an intrinsic semiconductor and Siltronic overview of Float Zone silicon growth.

Related Silicon Wafer & Research Resources

• Silicon Wafers
• Float Zone (FZ) Silicon Wafers
• High Resistivity Silicon Wafers
• Doped Silicon Wafers
• P-Type Silicon Wafers
• N-Type Silicon Wafers
• Silicon Wafer Resistivity
• Silicon Wafer Orientation
• Double Side Polished Silicon Wafers
• Thermal Oxide Silicon Wafers
• Silicon Wafer Applications
• Silicon Wafers for MEMS