GaN on Si for RF

GaN on Si for RF

GaN HEMT RF Epitxial Wafer on Si substrate, which is a wide bandgap semiconductor, can be offered by PAM-XIAMEN. The GaN HEMT on Si wafer has obvious advantages in the high-power, high-frequency application field. As for the GaN HEMT RF devices, they include PA, LNA, switch, MMIC, etc, which is mainly for base station satellite, radar and other markets.

1. RF GaN HEMT Structures on Silicon (GaN-based Heterostructures on Si-substrate)

No. 1 Epitaxial Structure for GaN HEMT RF Device

RF GaN HEMT on Si Wafer size 2″, 4″, 6″,8″
AlGaN/GaN HEMT structure Refer 1.2
Carrier density >9E12 cm2
Hall mobility /
Sheet Resistivity /
AFM RMS (nm)of 5x5um2 <0.25nm
Bow(um) <=30um
Edge exclusion  <5mm
SiN passivation layer  0~5nm
u-GaN cap layer  /
Al composition 20-30%
AlGaN barrier layer  /
GaN channel /
AlGaN buffer /
AlN /
Substrate material Silicon substrate
Si substrate resistivity (Ω cm) > 3000
Si wafer thickness (μm) 1000um(2″), 1000um(4″), 1300um(6″), 1500um(8″)


No. 2 GaN / Si HEMT Epi Structure for RF


4 inch GaN / Si HEMT Epi Structure for RF
Layer Material Thickness
4 AlGaN
3 AlN 0.5~1 nm
2 GaN (channel layer)
1 Buffer (Al,Ga)N
Substrate Si (111), 1000+/-25um thick, deflection < 50 um


Front side roughness: < 0.5 nm

Electro physical parameters are measured on control structures at room temperature (~25grad C):

 – Carrier concentration in the channel: >= 9*10^12 cm-2;

– Mobility in the channel:  1500~1700 cm¬2/V*s

– Resistivity of the buffer: > 10^5 Ohm*cm All parameters are measured at a distance > = 4 mm from the edge of the wafer.

Deviation of measured parameter values from required parameters: <= +/-10%.

No.3 GaN-on-Si HEMT Structure

PAMP20139 – HEMT

Layer No. Layer Name Material Thickness
5 Barrier layer In(0.17)Al(0.83)N
4 Interlayer AlN
3 Channel layer GaN
2 Back barrier In(0.15)Ga(0.85)N 2~3nm
1 RF buffer, Fe doped
Substrate 6-inch HR Si  


No. 4 GaN / Si based HEMT Structure

PAM200808 – HMET

Layer No. Layer Name Material Thickness
6 in-situ SiN
5 Barrier layer Al(0.23)Ga(0.77)N
4 Interlayer AlN
3 Channel layer GaN
2 Back barrier In(0.15)Ga(0.85)N 2~3nm
1 RF buffer
Substrate 6-inch HR Si    


No. 5 Si based GaN HEMT Epitaxial Wafer

PAM210201 – HEMT

Layer Material Thickness
4 SiN 10nm
3 AlGaN(25% Al)
2 GaN
1 Buffer (Fe-free)
Substrate High Res Si <111>, 6inch, 650-675um


* Electron mobility >1800cm2/Vs

* Sheet charge density >9E12cm-2

* Bow <50um


Features of GaN/Si Epiwafers for RF:
High uniformity and good repeatability;
Low RF loss

Typical Applications of GaN/Si Epiwafers:
5G and 6G wireless communications;
Solid-state RF energy application

2. About the GaN HEMT RF on Si Epi Wafer

The current industry production yield rate of on Si based GaN HEMT RF wafer is low. However, Si-based GaN HEMT price will be lower than that of SiC-based GaN HEMT because Si material is the most mature, defect-free, and lowest-cost substrate material; at the same time, Si can be expanded to 8-inch wafer fabs to reduce unit production costs.

In the RF PA market, the bandwidth of LDMOS PA will be greatly reduced as the frequency increases. It is only effective in the frequency range not exceeding about 3.5GHz. The frequency of GaN HEMT devices using 0.25 micron process can be as high as 4 times, and the bandwidth can be increased by 20%. The power density can reach 6~8 W/mm (LDMOS is 1~2W/mm), and the trouble-free working time can reach 1 million hours, which is more durable and has obvious advantages in comprehensive performance.

3. FAQ about RF GaN HEMT on Si Wafer

Q1: Could you provide us information about cleaning substrate backside from Ga contamination? Do you have TXRF data? We want to integrate GaN in our CMOS process and this moment is very important for us.

A: Our recommendation is that you can buy the epi wafer with substrate in backside oxide coating, after finishing epi growth, the backside oxide coating can be washed by pickling and exposed the original silicon substrate.

Q2: We are interested in buying GaN HEMT on Si for RF. I just have one question, you have mentioned a SiN passivation. Is this passivation in-situ ?

A: Yes, it is In-situ. RF GaN HEMT structure of 3nm Si3Nx cap without a GaN cap is available.

Q3: We have recently started processing devices on these InAlN/AlN/GaN HEMT structures and we find that the sheet resistance (Rs) values do not match with the specifications. In the test report (attached), Rs is mentioned as ~270-280 Ohm/sq on all these wafers. However, the devices processed on these wafers show an Rs of ~550 Ohm/sq (image attached). There is a gross mismatch between the quoted and the measured values! And we see this mismatch consistently on all the samples. Please let us know if the correct wafers are supplied.

A: The Rs data was tested by Lehighton Square resistance tester before shipping,and the Si-based GaN HEMT wafers are produced strictly according to the structure you offered.
Please note that InAlN is a very unstable barrier material. In particular, this structure has no cap layer protection, and there is a high probability of square resistance degradation nearly one year.

Q4: I had a quick question regarding the SiN cap for GaN/Si epi wafers. Is the SiN cap grown in-situ in the MOCVD reactor, or is it deposited with LPCVD/PECVD?

A: It is SiN cap grown in-situ on GaN HEMT wafer in the MOCVD reactor.


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