Self-Heating Profile in an AlGaN/GaN Heterojunction Field-Effect Transistor Studied by Ultraviolet and Visible Micro-Raman Spectroscopy

Abstract

Direct measurements of self-heating in gallium nitride (GaN) transistor using ultraviolet (UV) and visible micro-Raman spectroscopy are reported. The material stack was grown on silicon substrates and consists of an AlN nucleation, AlGaN transition, GaN buffer, and AlGaN barrier layers. Phonon shifts are used to estimate the temperature rise. UV measurements probe the current-carrying 2-D electron gas (2-DEG) in the GaN near the interface with the barrier region. Visible micro-Raman measurements provide an average temperature rise through GaN, AlN, and substrate near its interface with AlN. Together, these measurements provide a temperature depth profile. Under identical drive conditions, the increase in temperature from UV micro-Raman is approximately twice what is obtained from the visible measurements, reaching as high as 350°C above ambient temperature at input power of 7.8 W/mm. The temperature depth profile is simulated using finite-element analysis. We find that the temperature dependence of the thermal conductivity of GaN is important to incorporate in these simulations due to the large temperature rise in the 2-DEG region. A thermal boundary resistance of 1 × 10 −8 K · m 2 /W is obtained from the combined simulation and experimental results.

A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

“…The use of Raman spectroscopy for temperature measurements was first demonstrated on Si devices [29], but has been more fully exploited following the advancement of GaN electronic devices [30], and has since been demonstrated extensively by several groups [31][32][33][34][35]. This technique is often combined with finite element (FE) thermal simulation to determine the channel temperature, as well as the measurement of material thermal properties used for device thermal simulations [36][37][38].…”

“…where d 33 and d 31 are components of the piezoelectric modulus, E z is the vertical (aligned with the c-axis in GaN) component of electrical field, S 11 , S 12 and S 31 are components of the elastic compliance tensor, and b the phonon deformation potential. Figure 5(a) shows a simulated E z field distribution for an AlGaN/GaN HEMT, highlighting that the peak E z field is located at the gate foot.…”

“…Despite being experimentally challenging, time resolved Raman thermography measurements have also been applied to GaAs-based HEMTs [90]. For GaN electronic devices UV lasers have been used to measure the temperature in the GaN layer close to the 2DEG where Joule heating is generated [31,91].…”

Phonon properties and thermal conductivity of GaN nanofilm under prestress and surface/interface stress

“…GaN nanostructures are considered as a promising candidate for potential nanoelectronic devices such as optoelectronics, high-power electronics and ultrapower switches [3,4]. Thermal properties of GaN play an important role in these devices applications.…”

Ultraviolet and visible micro‐Raman and micro‐photoluminescence spectroscopy investigations of stress on a 75‐mm GaN‐on‐diamond wafer

“…In AlGaN/GaN high electron mobility transistors (HEMTs), the bulk of power production occurs within a 910 nm thick region of the two-dimensional electron gas (2DEG). This results in highly localized temperature rises, causing detrimental limitations to maximum operation power, output efficiency, and reliability [1,2]. For this reason, it is important to develop improvements for heat extraction near the active region of these devices.…”