Desorption Mass Spectrometry Techniques Research Articles

Desorption mass spectrometry: Revisiting the in-situ calibration technique for mixed group-V alloy MBE growth of ~3.3 µm diode lasers

We apply the desorption mass spectrometry (DMS) technique and analyze the desorbed Sb species in-situ during MBE growth of mixed As/Sb heterostructures. We demonstrate how DMS is useful in pre-growth calibration of the V/III ratio, the group-III ratio, as well as the Sb-content in quaternary or quinary mixed As/Sb alloys. We also apply DMS to the digital alloy growth method. For demonstration purposes, we start with an un-calibrated MBE system, use the DMS technique to calibrate all of the previously undetermined MBE parameters and grow a ~3.3µm diode laser heterostructure in only one attempt. The results demonstrate that the DMS technique will allow the MBE to quickly converge toward a set of acceptable growth parameters without the need for ex-situ calibration of alloy composition.

Desorption mass spectrometric control of composition during MBE growth of AlGaAs

We report on the implementation of technique of desorption mass spectrometry (DMS) in a real-time feedback loop for continuous monitoring and control of layer composition during molecular beam epitaxy growth of AlGaAs on (001) GaAs at high substrate temperatures. With this technique, the Ga desorption rate F d(Ga) and thus the composition is monitored continuously and kept at the desired value by adjusting either the substrate heater power or the incident arsenic flux. Composition control by DMS during growth of nominally constant composition layers is found to be superior to that obtained with conventional MBE growth, as indicated by F d(Ga) versus time profiles and low temperature photoluminescence (PL) results. The ability to produce complex graded structures by DMS control is demonstrated by the growth of nominally parabolic AlGaAs quantum wells, for which photoreflectance and PL results are consistent with the desired structure. The technique is quite general and applicable to many different compounds.

Arbitrary Composition Profiles by MBE Using Desorption Mass Spectrometry

ABSTRACTThe ability to produce semiconductor structures with arbitrary vertical composition profiles offers the device physicist new freedom in device structure design. We report on the incorporation of the in-situ sensor technique of desorption mass spectrometry (DMS) in a realtime feedback loop for the continuous control of desorption rates. Assuming previous knowledge of relevant incident fluxes, this technique provides for continuous determination of the composition of the outermost layer of the growing crystal. Using AlGaAs growth as an example, the Ga desorption rate Fd(Ga) is monitored continuously during growth, providing an accurate measure of Al-fraction in the topmost layer of the growing film. By comparing the measured and desired Fd(Ga), an error signal is generated and minimized by varying an appropriate growth parameter. Structures which are vertically graded in composition are produced by programming a varying Fd(Ga) versus time profile. Both substrate temperature Ts and incident arsenic flux Fi(As2) affect Fd(Ga) in a controllable way. Thus, two distinct control loops are constructed based on variable Ts and Fi(As2), respectively. As demonstration vehicles, graded AlGaAs structures with linear, parabolic, sawtooth, and sinusoidal compositional profiles have been produced and characterized. Additionally, we discuss some of the limitations of this technique and its applicability to other materials.