Tracing Zinc in InGaAs Heterostructures: Understanding Dopant Diffusion Across Buried Interfaces Using SIMS and HAXPES

A Closer Look at the Heterostructure

The sample under study featured two Zn-doped InGaAs layer atop an InP one, both 80 nm thick, which capped an 80 nm thick undoped InAlAs interlayer, the stack being grown over an InP substrate. This configuration is typical in high-speed or optoelectronic devices, where sharp interfaces and stable band alignments are critical for function.

To evaluate whether the InAlAs interlayer effectively confined zinc within the two top layers, the researchers performed SIMS profiling and electronic band mapping with HAXPES.

SIMS Depth Profiling Reveals Dopant Diffusion

Using a CAMECA IMS Xf series instrument equipped with a magnetic sector providing higher sensitivity than Time of flight (TOF) SIMS, the researchers performed SIMS depth profiling to measure ion signals for Zn, Ga, P, As, and In. These measurements provided a high-resolution picture of how zinc and matrix elements were distributed across the sample.

The SIMS data confirmed the Zn concentrations within the InGaAs and InP top layers, its intended location, but also a noticeable diffusion into the whole underlying InAlAs. This confirmed that this layer efficiently trapped and confined zinc from migrating downward under the growth conditions, preventing a diffusion into the N-doped InP substrate. Notably, Zn showed an accumulation at the InAlAs /InP interface.

The phosphorus profile served as a clear marker for identifying the InP layer and allowed the researchers to pinpoint where the diffusion front intersected with the layer boundaries. The other matrix element signals (gallium, arsenic, indium) remained consistent throughout profiling, indicating no modification of layer composition, thanks to good depth resolution and stable sputtering rate.

“Among the various techniques employed at the CEA-Grenoble NanoCharacterization Platform (PFNC), dynamic SIMS maintains a leading role in supporting the development of emerging nanotechnologies, thanks to its exceptional sensitivity and superior depth resolution.” — Marc Veillerot, Researcher, CEA LETI

HAXPES Confirms the Interface Abruptness

To complement the SIMS results concerning depth resolution, HAXPES measurements were carried out with a lab Quantes instrument from ULVAC-PHI equipped with a monochromatized Cr Kα X-ray source. Coupled with Ar+ pre-sputtering to reach the different interfaces, it was possible from In3d5/2, Ga2p3/2, As2p3/2 and P1s core levels to confirm the sharpness of the critical InGaAs/InP interface.

SIMS and HAXPES: A Complementary Approach

The study highlights how combining depth-resolved elemental analysis with electronic structure measurement can yield a more complete understanding of layer growth quality in semiconductor stacks. SIMS, especially using high-resolution magnetic sector instruments like the CAMECA IMS Xf series, proved crucial for tracking Zn migration with nanometer-scale accuracy. HAXPES, meanwhile, enabled a non-destructive look at how this redistribution might affect band alignment and charge transport.