Search

Herein, bandgap tuning of monoclinic (−201)‐oriented β‐(AlxGa1−x)2O3thin films is achieved through a β‐Ga2O3/Al2O3heterojunction by a feasible annealing process with an O2atmosphere. During the annealing process, Al atoms of the Al2O3substrate outdiffuse easily into the β‐Ga2O3thin film deposited by ozone‐assisted molecular beam epitaxy (OMBE). The Al compositions in the β‐(AlxGa1−x)2O3samples are tuned through adjusting the annealing temperature from 800 to 1300 °C and experimentally determined from the result of X‐ray photoelectron spectroscopy (XPS) measurements combined with Vegard's law. Successive Al‐composition‐gradient β‐(AlxGa1−x)2O3thin films with controlled bandgap are constructed. On these bases, β‐Ga2O3thin films are deposited on β‐(AlxGa1−x)2O3(0 ≤ x≤ 0.65) substrates through OMBE, yielding β‐Ga2O3/β‐(AlxGa1−x)2O3(0 ≤ x≤ 0.65) heterojunction structures, and the band offsets of this heterojunction are determined by XPS accordingly. This methodology to achieve high‐quality β‐(AlxGa1−x)2O3thin films with adjustable Al composition and tunable band offsets of the β‐Ga2O3/β‐(AlxGa1−x)2O3interface will provide guidance for potential strategies to develop and fabricate β‐(AlxGa1−x)2O3‐based deep‐UV photodetectors and power devices. Bandgap tuning of monoclinic (−201) oriented β‐(AlxGa1−x)2O3thin films are achieved through β‐Ga2O3/Al2O3heterojunction by a feasible annealing process. A successive Al composition‐gradient β‐(AlxGa1−x)2O3thin films with bandgap values controll are conducted. On these basis, β‐Ga2O3thin films are deposited on β‐(AlxGa1−x)2O3substrates through OMBE, yielding β‐Ga2O3/β‐(AlxGa1−x)2O3heterojunction structures, and the band offsets of this heterojunction are determined.

A low‐resistance Ohmic contact of Pd/Pt/Au metallization scheme is formed on a p‐type GaN film grown by metal‐organic chemical vapor deposition (MOCVD). Two samples are prepared to explore the effect of contaminations at the metal and GaN interface on the properties of the Ohmic contact. One directly transfers the fresh GaN film from MOCVD to the metal deposition chamber through an ultrahigh vacuum (UHV) tube, without exposing the GaN surface to air; the other transfers the GaN film from MOCVD to metal deposition through the atmosphere. The results show a lower specific contact resistance (6.2 ± 0.9) × 10−5Ω cm2for the directly UHV‐transferred sample than the air‐transferred sample (2.1 ± 0.9) × 10−4Ω cm2. Once exposed to air, carbonaceous particles and an amorphous oxide layer easily adhere to the p‐type GaN surface, which not only increase the Schottky barrier height but also generate more grain boundaries in the Pd/Pt/Au stacks. The grain boundaries, acting as diffusion channels, make Au atoms diffuse easily into the Pd layer and propagate to the p‐GaN surface layer after annealing. Therefore, the Ohmic contact fabricated in UHV ambience with lower oxygen and carbon contaminations at the interface shows superior characteristics than the samples prepared by the traditional method. Samples transferred via ultrahigh vacuum (UHV) with fewer contaminations at the interfaces of metal/GaN demonstrate lower specific contact resistance, higher reliability, and thermal stability than samples transferred through air with more C/O contaminations.

Growth mechanism and temperature of monoclinic gallium oxide (β‐Ga2O3) films grown by ozone molecular beam epitaxy (MBE) are investigated herein. Phase‐pure (2¯01) β‐Ga2O3films can be grown on c‐plane sapphire substrates when the growth temperature exceeds 500 °C, and the grain size increases with the increase in the growth temperature. Sixfold rotational domains are obtained based on the epitaxial relationships (Ga2O3< 010>//Al2O3<11¯00> and Ga2O3< 102>//Al2O3< 112¯0>). For the film grown at 700 °C, the threefold facets are observed for the first time, which are resulted from the easy‐cleaved (100) plane and rotational domains. In addition, the cathodoluminescence spectra of the β‐Ga2O3films show that the proportion of ultraviolet emission increases with the increase in the growth temperature, which is attributed to the modulation of defect. Finally, the growth rate can be modulated by the ratio of Ga flux and ozone pressure. A reference is provided for heteroepitaxy of β‐Ga2O3films and better understanding of the ozone MBE growth mechanism of oxides. β‐gallium oxide (β‐Ga2O3) films are grown on c‐plane sapphire substrates using molecular beam epitaxial technique with pure ozone as the oxygen source. For the film grown at 700 °C, threefold facets are first observed as the distinct feature of surface morphology, which can be formed due to the easy‐cleaved (100) plane and rotational domains.