At Ferdinand-Braun-Institute (FBH) in Berlin
LayTec's EpiCurve®TT HR (High Resolution) sensor is successfully used
to optimise the external quantum efficiency and the emission wavelength of LEDs
for near UV spectral region. Dr. Arne Knauer and co-workers apply the sensor
for monitoring of composition of AlGaN and InAlGaN barrier layers.
Since the Indium incorporation is highly sensitive to the temperature,
small changes of the surface temperature caused
e.g. by the wafer bow during growth can result in large variations
of the In content in the InAlGaN layers. The team at FBH
grew multiple quantum well (MQW) structures with GaN, Al-
GaN and InAlGaN barriers with different In content (between
0% and 5%) and compared the wafer curvature of the calibration
layers and of the multiple quantum well (MQW) barrier
layers. Fig. 2 shows the development of the curvature signal
during the deposition of barrier layers with different compositions
stemming from different growth runs.
The growth of nearly unstrained GaN and of In0.03Al0.16Ga0.81N
barriers (red curve) results in a nearly constant curvature.
The In0.05Al0.16Ga0.79N barriers (green curve) grow under compression
and therefore the curvature signal decreases. The
Al0.16Ga0.84N barriers (black curve) are under tensile stress and
the curvature increases. This data demonstrates the possibility
to monitor not only stress, but also the composition of
extremely thin layers (8 nm).
The results of the study have been submitted for publication
in Physica status solidi, Proceedings of the 3rd International
Symposium on Semiconductor Light Emitting Devices
(ISSLED) Phoenix, USA, April 27-May 2, 2008. For further information
please contact [email protected]