Comparison of MOCVD and MBE Regrowth for CAVET Fabrication

Abstract

In this paper, we demonstrate the fabrication of current aperture vertical electron transistors (CAVET) realized with two different epitaxial growth methods. Templates with a p-GaN current blocking layer (CBL) were deposited by metal organic chemical vapor deposition (MOCVD). Channel and barrier layers were then regrown by either molecular beam epitaxy (MBE) or MOCVD. Scanning electron microscope (SEM) images and atomic force microscope (AFM) height profiles are used to identify the different regrowth mechanisms. We show that an AlN interlayer below the channel layer was able to reduce Mg diffusion during the high temperature MOCVD regrowth process. For the low-temperature MBE regrowth, Mg diffusion was successfully suppressed. CAVET were realized on the various samples. The devices suffer from high leakage currents, thus further regrowth optimization is needed.

Metal organic chemical vapour deposition regrown large area GaN‐on‐GaN current aperture vertical electron transistors with high current capability

“…The measured absolute current of the vertical comb structures is comparable to published values for lateral HEMT structures with the same layout [6]. However, the device reveals a turn‐on voltage of around 3 V. Such effect has previously been observed in earlier publications [1, 4]. A partial depletion in the aperture due to the lateral pn‐junction (CBL‐aperture) has been assumed in [4] but the exact mechanism underlying this effect is still under investigation.…”

“…However, the device reveals a turnon voltage of around 3 V. Such effect has previously been observed in earlier publications [1,4]. A partial depletion in the aperture due to the lateral pn-junction (CBL-aperture) has been assumed in [4] but the exact mechanism underlying this effect is still under investigation. The high on-state resistance and the high saturation voltage V D,SAT in the fabricated devices are assumed to be a result of low effective carrier concentration in the nominally undoped aperture and drift region.…”

“…Additionally, the breakdown voltage in the published devices has been a critical issue, due to very high leakage currents [2–4], which was successfully addressed in this work. However, the results of our large CAVETs indicate a reduction in current density J , when compared to results of small CAVETs published in [1, 2, 4].…”

“…Mg-implantation to form the CBL seems to be an advantageous process, as the aperture region remains unaffected and only one (planar) regrowth step is necessary to fabricate the CAVET structure. Moreover, the breakdown voltage has been an issue in CAVET structures fabricated by SAG, aperture implantation or nonplanar regrowth [2][3][4]. However, CAVETs using Mg-implantation were only demonstrated by separate post-annealing of the Mg-implanted CBL and subsequent MBE regrowth yet [1].…”

“…This has mostly been addressed by molecular beam epitaxy (MBE) regrowth of the GaN‐channel, as the lower growth temperature with respect to MOCVD allows for much sharper doping profiles. Small gate width transistors were published in CAVET technology using Mg‐implantation [1] or selective area regrowth [2] of the CBL, Si‐implantation of the aperture region [3] or by overgrowth of an etched aperture [4]. Mg‐implantation to form the CBL seems to be an advantageous process, as the aperture region remains unaffected and only one (planar) regrowth step is necessary to fabricate the CAVET structure.…”