In the next years, the use of PSS will further increase due to its high light extraction efficiency. Following this trend, LayTec‘s in-situ metrology software EpiNet 2 can be individually customized for various kinds of PSS. Our users can expand the substrate database by themselves. LayTec‘s Calibration Manual explains how to measure PSS reflectance in different pockets in one single calibration run. If required, LayTec also offers related customer trainings. Once the initial reflectance values of the PSS substrates are uploaded, the operator can choose the needed substrate in the RunType‘s Material Spec window (Fig. 1). As a result, all PSS wafers can be monitored with the same accuracy as standard sapphire substrates.


Fig. 1: Extract of a Run-Type’s Material Spec window of LayTec‘s EpiNet 2 software with a customized database extended by additional PSS types.

Fig. 2 shows a GaN growth on PSS. The initial 405 nm reflectance on the bare PSS substrate is „noisy“ because it senses the local non-uniformity of the PSS structure. As soon as GaN buffer is thick enough, this „noise“ reduces because the 405 nm light does not reach the PSS pattern anymore through the UV absorbing GaN. The increasing reflectance of all 3 wavelengths after ~4000 s shows the coalescence process of GaN. After ~8050 s, the 405 nm reflectance stays stable at 15.5%, which is an indication of the GaN surface quality improvement. However, the interference patterns of the 633/950 nm reflectance look „noisy“ during 2 D buffer growth. Obviously, the initial non-uniformity of the PSS structure causes a certain non-uniformity in the GaN thickness.


Fig. 2: GaN growth on PSS measured by EpiCurve®TT at FBH, Berlin, Germany: reflectance at 405 nm (blue), 633 nm (green), 950 nm (red); True Temperature (black).

Alongside with the customized database, EpiNet 2 also provides fitting of thin layers, wafer bow calculation and many further features indispensable for growth on PSS. Learn more in EpiNet 2 datasheet by contacting sales@laytec.de.