## 1 Introduction  
The Si-based complementary logic integrated circuits (ICs) are showing the drawbacks of large leakage currents or poor reliabilities in harsh environments, especially for high-power applications. On the other hand, GaN-based field effect transistors (FETs) can achieve a much higher breakdown voltage and faster switching speed than Si FETs benefitting from their higher mobility at the heterojunctions, larger saturation velocity, higher breakdown voltages, and higher thermal and chemical stability [1; 2; 3]. To efficiently drive and control the GaN-based power electronic devices, the ultimate choice is to utilize one-chip CMOS logic circuits with both \(n\)-channel and \(p\)-channel FETs [4]. However, compared with the rapid development in the \(n\)-channel AlGaN/GaN high electron mobilitytransistors (HEMTs) using the two-dimensional electron gas (2 DEG), little attention has been paid to the \(p\)-channel FETs with the two-dimensional hole gas (2 DHG). Actually, the 2 DHG channel in the AlGaN and AlInGaN-based heterostructures has been expected according to the polarization theory [5; 6; 7; 8; 9]. In the III-V nitride family, an InGaN/GaN heterojunction could offer a better route for the \(p\)-channel transistors compared to the AlGaN system in terms of a much lower on-resistance because of its lower activation energy of Mg and hole effective mass [10; 11]. InGaN has the highest piezoelectric polarization coefficient among all the III-V nitride materials, which is beneficial for the generation of high-density 2 DHG in the conducting channel [12]. More importantly, the utilization of InGaN/GaN \(p\)-channel structures can avoid the crack problem when grown on AlGaN/GaN \(n\)-channel transistors as a result of the in-plane compressive strain. In 2015, our group has successfully achieved 2 DHG at the InGaN/GaN heterostructure on the sapphire substrate, and fabricated \(p\)-channel metal-oxide-semiconductor (MOS) FETs, which can be operated from cryogenic to room temperature [2]. To realize the CMOS circuits, it is better to deposit the \(p\)-channel transistors on the \(n\)-channel AlGaN/GaN template. In this regard, the AlGaN/GaN-on-Si HEMT template will be promising due to its lower cost and better integration with Si electronics. Unfortunately, as a result of the large lattice mismatch between AlGaN and InGaN, it is still difficult to obtain high-performance \(p\)-channel FETs on HEMT/Si structures. To achieve a high mobility and hole concentration, the high-quality InGaN/GaN heterojunction with a high crystalline quality and good interface is necessary to avoid the dislocation and alloy disorder scattering. Therefore, the optimization in the epitaxial growth and the property investigation of InGaN/GaN on the HEMT/Si template is necessary and in great demand.  
In this work, we systematically investigate and analyze the growth, and structural and optical properties of InGaN/GaN heterostructures grown on the commercial AlGaN/GaN-on-Si HEMT templates by comparing with those grown on the GaN/sapphire templates. It is found that the strain state and indium incorporation in the heterojunctions are quite different even if they are grown at the same conditions. The crystalline quality of the InGaN/GaN heterojunction is dependent on the quality of the templates. The optimization on the growth condition can improve the interface and crystalline quality of the InGaN/GaN heterojunction.