Calculation of the Energy Band Diagram and Estimation of Electronic Transport Parameters of Metastable Amorphous Ge2Sb2Te5

Oct 29, 2026

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We calculate critical electronic conduction parameters for metastable amorphous Ge2Sb2Te5 (GST), a phase-change-memory material. A temperature-dependent energy band model yields the room-temperature bandgap Eg(300K)=1.84 eV. Using latent heat of fusion and thin-film melt resistivity, we estimate carrier density and mobility at melting, and model bipolar conduction to derive free-carrier concentrations at 300K. We further infer that the stable drifted amorphous GST exhibits p-type conduction with p(300K)≈6×10^16 cm^-3.

LanguageEnglish

CategoryResearch & Report

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Pages8

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Introduction

Results and Discussion

Temperature dependent energy band model

Calculation of the Energy Band Diagram and Estimation of Electronic Transport Parameters of Metastable Amorphous Ge2Sb2Te5 M. T. B. Kashema, S. Muneera,b, L. Adnanea,c, F. Dirisaglika,d, A. Gokirmaka, and H. Silvaa a Department of Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut 06269, USA b Department of Electrical and Electronic Engineering, United International University, Dhaka 1212, Bangladesh c Analog Devices, Boston, MA, USA d Department of Electrical and Electronics Engineering, Eskisehir Osmangazi University, Eskisehir 26480, Turkey We calculate critical electronic conduction parameters of the amorphous phase of Ge2 Sb2Te5 (GST), a common material used in phase change memory. We estimate the room temperature bandgap of metastable amorphous GST to be Eg (300K) = 1.84 eV based on a temperature dependent energy band model. We estimate the free carrier concentration at the melting temperature utilizing the latent heat of fusion to be 1.47 x 1022 cm-3. Using the thin film melt resistivity, we calculate the carrier mobility at melting point as 0.187 cm2/V-s. Assuming that metastable amorphous GST is a supercooled liquid with bipolar conduction, we compute the total carrier concentration as a function of temperature and estimate the room temperature free carrier concentration as p(300K) ≈ n(300K)= 1.69×10 17 cm-3. Free electrons and holes are expected torecombine over time and the stable (drifted) amorphous GST is estimated to have p-type conduction with p(300K) ≈ 6×1016 cm-3. Introduction Phase change memory (PCM) is a high speed, high density non-volatile resistive memory technology that utilizes different phases (crystalline and amorphous) of phase change materials to store information (1,2) . The material undergoes two types of switching phenomena: (i) Ovonic Threshold Switching (OTS), which causes the amorphous phase of the material to switch from a highly resistive state to a conductive state with application of high electric fields, resulting in substantial current flow and (ii) Ovonic Memory Switching (OMS), which is the non-volatile change of the phase of the material between amorphous and crystalline phases induced by heating (3) . The chalcogenide alloy Ge2 Sb2Te5 (GST) is the most commonly used phase change material in PCM due to its rapid and repeatable phase change capability, high resistance contrast between amorphous and crystalline phases and high stability (4-8) . Though many studies have been reported regarding the atomic configuration (9-11) and optical properties (12,13) of GST, the electronic properties are still not well understood (14,15) . In this work, we extract several electronic conduction parameters of amorphous GST (a-GST) from experimental data. We use the activation energy of conduction (16) to calculate the temperature dependent energy band diagram of metastable a-GST assuming the energy bandgap shrinks linearly with temperature. We calculate the carrier concentration and mobility at the melting temperature from the reported latent heat of fusion of the material (17) and thin film melt resistivity (18) . Assuming the carrier mobility to be weakly varying with temperature and bipolar conduction for the intrinsic material, we estimate the total carrier concentration in a wide temperature range using the device level measured resistivity for GST line cells (19) . Results and Discussion Temperature dependent energy band model We have previously determined the effective activation energy of conduction, 􀜧􀯔 for metastable a-GST (16) (Figure 1a) utilizing the resistivity (ρ) versus temperature (T) data obtained from high-speed electrical measurements on nanoscale GST line cells (19) . Using a reference 􀜧􀯔 = 32 􀝇􀮻 􀜶 at the melting temperature (Tmelt), where 􀝇􀮻 is the Boltzmann constant, we obtained 􀜧􀯔 = 0 at ~ 930K, which we identified as the transition temperature from liquid-semiconducting to liquid-metallic phase of the materia

FAQs

What material and phase are analyzed in the study?

The study analyzes metastable amorphous Ge2Sb2Te5 (a-GST), a key phase-change material used in phase change memory.

How is the room-temperature bandgap Eg(300K) estimated?

A temperature-dependent energy band model is used, producing Eg(300K)=1.84 eV.

How are carrier concentration and mobility at the melting temperature obtained?

Carrier concentration is estimated using the latent heat of fusion, and mobility at melting is calculated from thin-film melt resistivity.

Oct 29, 2026

Upload by Elsa